docs: add dev instructions to README (#155)

Co-authored-by: Mitchell Hanberg <[email protected]>

Author: crbelaus

README.md

@@ -66,6 +66,30 @@ The preferred way to use Next LS is through one of the supported editor extensio
 
 If you need to install Next LS on it's own, you can download the executable hosted by the GitHub release. The executable is an Elixir script that utilizes `Mix.install/2`.
 
+## Development
+
+If you are making changes to NextLS and want to test them locally you can run
+`bin/start --port 9000` to start the language server (port 9000 is just an
+example, you can use any port that you want as long as it is not being used
+already).
+
+Then you can configure your editor to connect to NextLS using that port.
+
+[elixir-tools.nvim](https://github.com/elixir-tools/elixir-tools.nvim)
+
+```lua
+{
+  nextls = {enable = true, port = 9000}
+}
+
+Visual Studio Code
+
+```json
+{
+    "elixir-tools.nextls.adapter": "tcp",
+    "elixir-tools.nextls.port": 9000,
+}
+
 ### Note
 
 Next LS creates an `.elixir-tools` hidden directory in your project, but it will be automatically ignored by `git`.