docs: split wiki content appropriately

- Move 'Developing mocha' wiki content to .github/DEVELOPMENT.md
- Keep 'Using Mocha programmatically' in public docs

Author: TG199

.github/DEVELOPMENT.md

@@ -16,3 +16,22 @@ If you are having trouble, don't be afraid to [ask for help](./CONTRIBUTING.md#
    - Do not use `yarn install` or `pnpm install`.
    - Some optional dependencies may fail; you can safely ignore these unless you are trying to build the documentation.
    - If you're sick of seeing the failures, run `npm install --ignore-scripts`.
+
+## Developing Mocha
+
+When you contribute to mocha, you will probably want to try to run your changes on the test suite of another project. You can (and should) run the test suite of mocha itself before committing, but also confirming that your changes give the expected result on another project.
+
+For example, [WebSocket.io](https://github.com/LearnBoost/websocket.io/):
+
+    $ git clone https://github.com/LearnBoost/websocket.io.git
+
+Retreive websocket.io's dependencies, which will include the stable version of mocha:
+
+    $ cd websocket.io/
+    $ npm install
+
+Replace the mocha dependency by the current git repository:
+
+    $ cd node_modules/
+    $ mv mocha/ mocha.save
+    $ git clone https://github.com/visionmedia/mocha.git