docs: consolidate 'Source Code' page into 'Set up Development Environ…

…ment' page

Resolves #16775

docs/src/contribute/development-environment.md

@@ -15,10 +15,16 @@ Go to <https://nodejs.org/> to download and install the latest stable version fo
 
 Most of the installers already come with [npm](https://www.npmjs.com/) but if for some reason npm doesn't work on your system, you can install it manually using the instructions on the site.
 
-## Step 2: Fork and checkout your own ESLint repository
+## Step 2: Fork and Checkout Your Own ESLint Repository
 
 Go to <https://github.com/eslint/eslint> and click the "Fork" button. Follow the [GitHub documentation](https://help.github.com/articles/fork-a-repo) for forking and cloning.
 
+Clone your fork:
+
+```shell
+git clone https://github.com/<Your Github Username>/eslint
+```
+
 Once you've cloned the repository, run `npm install` to get all the necessary dependencies:
 
 ```shell
@@ -28,7 +34,9 @@ npm install
 
 You must be connected to the Internet for this step to work. You'll see a lot of utilities being downloaded.
 
-## Step 3: Add the upstream source
+**Note:** It's a good idea to re-run `npm install` whenever you pull from the main repository to ensure you have the latest development dependencies.
+
+## Step 3: Add the Upstream Source
 
 The *upstream source* is the main ESLint repository where active development happens. While you won't have push access to upstream, you will have pull access, allowing you to pull in the latest code whenever you want.
 
@@ -56,7 +64,7 @@ npm install -g generator-eslint
 
 Please see the [generator documentation](https://github.com/eslint/generator-eslint) for instructions on how to use it.
 
-## Step 5: Run the tests
+## Step 5: Run the Tests
 
 Running the tests is the best way to ensure you have correctly set up your development environment. Make sure you're in the `eslint` directory and run:
 
@@ -68,6 +76,21 @@ The testing takes a few minutes to complete. If any tests fail, that likely mean
 
 ## Reference Information
 
+### Directory Structure
+
+The ESLint directory and file structure is as follows:
+
+* `bin` - executable files that are available when ESLint is installed
+* `conf` - default configuration information
+* `docs` - documentation for the project
+* `lib` - contains the source code
+    * `formatters` - all source files defining formatters
+    * `rules` - all source files defining rules
+* `tests` - the main unit test folder
+    * `lib` - tests for the source code
+        * `formatters` - tests for the formatters
+        * `rules` - tests for the rules
+
 ### Workflow
 
 Once you have your development environment installed, you can make and submit changes to the ESLint source files. Doing this successfully requires careful adherence to our [pull-request submission workflow](./pull-requests).