Add usage and test documentation

This updates the README and adds documentation on how to edit and test the Terraform tmGrammar.

It copies some wording from the vscode-terraform project.

DEVELOPMENT.md

@@ -0,0 +1,72 @@
+# Development
+
+We are an open source project on GitHub and would enjoy your contributions! Please [open a new issue](https://github.com/hashicorp/syntax/issues) before working on a PR that requires significant effort. This will allow us to make sure the work is in line with the project's goals.
+
+### Requirements
+
+- Node >= 16.13.2
+- npm >= 8.x
+
+### Getting the code
+
+```bash
+git clone https://github.com/hashicorp/syntax
+```
+
+### Dependencies
+
+After cloning the repo, run `npm install` to install dependencies.
+
+```bash
+npm install
+```
+
+## Writing TextMate Grammar
+
+The following workflow is recommended to work on Terraform TextMate grammar:
+
+1. Add or modify grammar to the `terraform.tmGrammar.json` file inside the `syntaxes` directory.
+1. Add a new unit test file or modify existing unit test files inside the test/unit/terraform directory.
+1. Run `npm run test:grammar` until the tests pass
+1. Add a new example Terraform file or modify existing unit test files inside the test/snapshot/terraform directory.
+1. Run `npm run test:snap` until the tests pass. 
+
+> Tip: Running `npm run test:snap -- -u` after modifying the tmGrammar file will give you a quick visual representation of how the tokens are being resolved. This can aid in crafting unit tests.
+
+## Tests
+
+Automated `unit` tests can be written using [vscode-tmgrammar-test](https://github.com/PanAeon/vscode-tmgrammar-test) and live inside `./tests`.
+
+To start the test suite from the command-line run:
+
+```bash
+npm test:unit
+```
+
+## Writing Grammar Unit Tests
+
+Unit tests are Terraform files with `vscode-tmgrammar-test` token lines specifying which TextMate grammer should be resolved.
+
+For example:
+
+> Note: This is shortened to demonstrate, actual syntax will vary
+
+```
+resource "example" "thing" {
+;         ^^^^^^^ source.terraform string.quoted.double.terraform
+;                   ^^^^^ source.terraform string.quoted.double.terraform
+;                          ^ source.terraform punctuation.section.block.begin.terraform
+}
+; <- source.terraform punctuation.section.block.end.terraform
+
+```
+
+## Writing Grammar Snapshot Tests
+
+Snapshot tests comprise of two files: example files and their companion `snap` file.
+
+Snapshot test example files are Terraform files without any `vscode-tmgrammar-test` token lines. Each example file is exactly how you would see it used in production. This ensures scope, inheritance, and resolution of tokens happen exactly as they would on a user's machine.
+
+The companion `snap` file is named the same as the example file with the `.snap` extension, and is the tmGrammar represenation of all resolved tokens. This file is commited alongside the example file. If anything changes with regards to how the tokens are resolved, the snapshot test will fail.
+
+> Note: If modifying an existing snapshot test, run `npm run test:snap -- -u` to update the snapshot file. This will update the snapshot file with the new modified grammar. Be sure to do this after you've tested using `npm run test:grammar` and are sure that the modified grammar is correct, otherwise you may get false positives.

README.md

@@ -1,4 +1,6 @@
-# Syntax
+# HashiCorp Syntax
+
+Syntax highlighting files for editors (VSCode, SublimeText, TextMate, etc.) for the Terraform Language
 
 ## Files included
 
@@ -8,14 +10,8 @@ By product, format:
 
 ## What editors this can be used with
 
-Yes: [VSCode](https://code.visualstudio.com/api/language-extensions/syntax-highlight-guide), [Sublime Text](https://www.sublimetext.com/docs/3/syntax.html)
-
-Maybe: [IntelliJ](https://www.jetbrains.com/help/idea/tutorial-using-textmate-bundles.html)
-
-No: vim
-
-## Other uses
-
-TBA
-
-<!-- i.e. https://github.com/github/linguist -->
+Editor | Supported
+-- | --
+[VSCode](https://code.visualstudio.com/api/language-extensions/syntax-highlight-guide) | ✅
+[Sublime Text](https://www.sublimetext.com/docs/3/syntax.html) | ✅
+[IntelliJ](https://www.jetbrains.com/help/idea/tutorial-using-textmate-bundles.html) | 🔧