update contribute (#2011)

CONTRIBUTING.md

@@ -0,0 +1,33 @@
+# How to Contribute to CMake Tools
+
+This article is for developers who want to contribute to the CMake Tools open source project.
+
+## Build the CMake Tools extension
+
+As with most VS Code extensions, you'll need [Node.JS](https://nodejs.org/en/) installed. We use [yarn](https://yarnpkg.com/getting-started/install) to compile the code.
+
+The process is:
+
+1. Open the repo in VS Code
+
+2. Press <kbd>F5</kbd> to build and run the extension
+
+## Coding guidelines
+
+### Formatting
+
+Code is formatted using `clang-format`. We recommend you install the
+[Clang-Format extension](https://marketplace.visualstudio.com/items?itemName=xaver.clang-format).
+
+### Linting
+
+We use eslint for linting our sources.
+You can run `eslint` across the sources from a terminal or command prompt by running `yarn run lint`.
+Warnings from `eslint` show up in the **Errors and Warnings** pane and you can navigate to them from inside VS Code.
+To lint the source as you make changes, install the [eslint extension](https://marketplace.visualstudio.com/items?itemName=dbaeumer.vscode-eslint).
+
+### Style [Updated!]
+
+Follow the [Typescript Coding guidelines](https://github.com/Microsoft/TypeScript/wiki/Coding-guidelines).
+
+> `snake_case` was used historically for variables in this repo, but that style is phased out. All new variables should be `lowerCamelCase`.