Add issue and PR templates, clarify guidelines (#1297)

Author: dcodeIO

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,4 @@
+<!--
+ Thanks for submitting an issue to AssemblyScript! Please take a moment to
+ read the contributing guidelines linked below to get off to a good start 🙂
+-->

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,10 @@
+<!--
+ Thanks for submitting a pull request to AssemblyScript! Please take a moment to
+ review the contributing guidelines linked below, and confirm with an [x] 🙂
+-->
+
+⯈
+⯈
+⯈
+
+- [ ] I've read the contributing guidelines

CONTRIBUTING.md

@@ -35,15 +35,20 @@ Submitting Pull Requests
 
 Instructions are similar to those for bug reports. Please provide the following information:
 
+* If this is not a trivial fix, consider **creating an issue to discuss first** and **later link to it from the PR**.
 * Use a **clear and descriptive title** for the pull request.
-* Provide a **description of the suggested changes** in as many details as necessary.
+* Provide a **description of the changes** in as many details as necessary.
 * **Document your new code** where necessary.
 * Please **refrain from refactoring (unrelated code)** as it makes your pull request easier to review.
 * **Create tests for your new code** where necessary. For creating or updating tests, please see the [Test Instructions](./tests).
 
-Before submitting your pull request, please make sure that the following conditions are met:
+Before submitting your pull request, also make sure that the following conditions are met:
 
 * Your new code **adheres to the code style** through running `npm run check`.
 * Your new code **passes all existing and new tests** through running `npm run test`.
 * Your PR **excludes distribution files** in `dist/**`.
 * You appended yourself to the **list of contributors** in the [NOTICE](./NOTICE) file.
+
+Please note that if a pull request is rather complicated, i.e. touches lots of internals, or became stale, it is not uncommon that a core contributor performs the final integration to get it done in good conscience while naming you as a co-author.
+
+Thank you!