docs: Add embed gist instructions to Embed Files (fixes #932 ) (#1238)

* Clarify embed file explanations

* Add Embed a gist section

* Update gist instructions

* Fix grammar errors and clarify notes around gists

* Add real gist to embed-files.md

* Clean up embed-files.md

Author: MichaelCurrin

Diff for: docs/embed-files.md

@@ -1,41 +1,44 @@
 # Embed files
 
 With docsify 4.6 it is now possible to embed any type of file.
+
 You can embed these files as video, audio, iframes, or code blocks, and even Markdown files can even be embedded directly into the document.
 
-For example, here embedded a Markdown file. You only need to do this:
+For example, here is an embedded Markdown file. You only need to do this:
 
 ```markdown
 [filename](_media/example.md ':include')
 ```
 
-Then the content of `example.md` will be displayed directly here
+Then the content of `example.md` will be displayed directly here;
 
 [filename](_media/example.md ':include')
 
 You can check the original content for [example.md](_media/example.md ':ignore').
 
 Normally, this will compiled into a link, but in docsify, if you add `:include` it will be embedded.
 
+External links can be used too - just replace the target. If you want to use a gist URL, see [Embed a gist](#embed-a-gist) section.
+
 ## Embedded file type
 
-Currently, file extension are automatically recognized and embedded in different ways.
+Currently, file extensions are automatically recognized and embedded in different ways.
 
-This is a supported embedding type:
+These types are supported:
 
 * **iframe** `.html`, `.htm`
 * **markdown** `.markdown`, `.md`
 * **audio** `.mp3`
 * **video** `.mp4`, `.ogg`
 * **code** other file extension
 
-Of course, you can force the specified. For example, you want to Markdown file as code block embedded.
+Of course, you can force the specified type. For example, a Markdown file can be embedded as a code block by setting `:type=code`.
 
 ```markdown
 [filename](_media/example.md ':include :type=code')
 ```
 
-You will get it
+You will get:
 
 [filename](_media/example.md ':include :type=code')
 
@@ -91,3 +94,78 @@ Embedding any type of source code file, you can specify the highlighted language
 [](_media/example.html ':include :type=code text')
 
 ?> How to set highlight? You can see [here](language-highlight.md).
+
+## Embed a gist
+
+You can embed a gist as markdown content or as a code block - this is based on the approach at the start of [Embed Files](#embed-files) section, but uses a raw gist URL as the target.
+
+?> **No** plugin or app config change is needed here to make this work. In fact, the "Embed" `script` tag that is copied from a gist will _not_ load even if you make plugin or config changes to allow an external script.
+
+### Identify the gist's metadata
+
+Start by viewing a gist on `gist.github.com`. For the purposes of this guide, we use this gist:
+
+- https://gist.github.com/anikethsaha/f88893bb563bb7229d6e575db53a8c15
+
+Identify the following items from the gist:
+
+Field               | Example                            | Description
+---                 | ---                                | ---
+**Username**        | `anikethsaha`                      | The gist's owner.
+**Gist ID**         | `c2bece08f27c4277001f123898d16a7c` | Identifier for the gist. This is fixed for the gist's lifetime.
+**Filename**        | `content.md`                       | Select a name of a file in the gist. This needed even on a single-file gist for embedding to work.
+
+You will need those to build the _raw gist URL_ for the target file. This has the following format:
+
+- `https://gist.githubusercontent.com/USERNAME/GIST_ID/raw/FILENAME`
+
+Here are two examples based on the sample gist:
+
+- https://gist.githubusercontent.com/anikethsaha/f88893bb563bb7229d6e575db53a8c15/raw/content.md
+- https://gist.githubusercontent.com/anikethsaha/f88893bb563bb7229d6e575db53a8c15/raw/script.js
+
+?> Alternatively, you can get a raw URL directly clicking the _Raw_ button on a gist file. But, if you use that approach, just be sure to **remove** the revision number between `raw/` and the filename so that the URL matches the pattern above instead. Otherwise your embedded gist will **not** show the latest content when the gist is updated.
+
+Continue with one of the sections below to embed the gist on a Docsify page.
+
+### Render markdown content from a gist
+
+This is a great way to embed content **seamlessly** in your docs, without sending someone to an external link. This approach is well-suited to reusing a gist of say installation instructions across doc sites of multiple repos. This approach works equally well with a gist owned by your account or by another user.
+
+Here is the format:
+
+```markdown
+[LABEL](https://gist.githubusercontent.com/USERNAME/GIST_ID/raw/FILENAME ':include')
+```
+
+For example:
+
+```markdown
+[gist: content.md](https://gist.githubusercontent.com/anikethsaha/f88893bb563bb7229d6e575db53a8c15/raw/content.md ':include')
+```
+
+Which renders as:
+
+[gist: content.md](https://gist.githubusercontent.com/anikethsaha/f88893bb563bb7229d6e575db53a8c15/raw/content.md ':include')
+
+The `LABEL` can be any text you want. It acts as a _fallback_ message if the link is broken - so it is useful to repeat the filename here in case you need to fix a broken link. It also makes an embedded element easy to read at a glance.
+
+### Render a codeblock from a gist
+
+The format is the same as the previous section, but with `:type=code` added to the alt text. As with the [Embedded file type](#embedded-file-type) section, the syntax highlighting will be **inferred** from the extension (e.g. `.js` or `.py`), so you can leave the `type` set as `code`.
+ 
+Here is the format:
+
+```markdown
+[LABEL](https://gist.githubusercontent.com/USERNAME/GIST_ID/raw/FILENAME ':include :type=code')
+```
+
+For example:
+
+```markdown
+[gist: script.js](https://gist.githubusercontent.com/anikethsaha/f88893bb563bb7229d6e575db53a8c15/raw/script.js ':include :type=code')
+```
+
+Which renders as:
+
+[gist: script.js](https://gist.githubusercontent.com/anikethsaha/f88893bb563bb7229d6e575db53a8c15/raw/script.js ':include :type=code')