Update getting-started.md

docs/internals/getting-started.md

@@ -32,4 +32,42 @@ If you're not core developer or want to use your own fork for pull requests:
 > Hint: The workflow of forking a package and pushing changes back into your fork and then sending a pull-request to the
   maintainer is the same for all extensions you require via composer.
 
-Please refer to [Git workflow for Yii 2 contributors](git-workflow.md) for details about creating pull requests.
\ No newline at end of file
+Please refer to [Git workflow for Yii 2 contributors](git-workflow.md) for details about creating pull requests.
+
+
+An Alternative way
+------------------
+
+1. Clone your fork of yii2 `git clone git@github.com:<yourname>/yii2`.
+2. Change into the repo folder `cd yii2`.
+3. run `./build/build app/link basic` to install composer dependecies for the basic app.
+   This command will install foreign composer packages as normal but will link the yii2 repo to
+   the currently checked out repo, so you have one instance of all the code installed.
+4. Do the same for the advanced app if needed: `./build/build app/link advanced`
+   This command will also be used to update dependecies, it runs `composer update` internally.
+5. Now you have a working playground for hacking on Yii 2.
+
+You may also add the yii2 upstream repo to pull the latest changes:
+
+```
+git remote add upstream https://github.com/yiisoft/yii2.git
+```
+
+### Unit tests
+
+To run the unit tests you have to install composer packages for the dev-repo.
+Run `composer update` in the repo root directory to get the latest packages.
+
+You can now execute unit tests by running `./vendor/bin/phpunit`.
+
+You may limit the tests to a group of tests you are working on e.g. to run only tests for the validators and redis
+`./vendor/bin/phpunit --group=validators,redis`.
+
+### Extensions
+
+To work on extensions you have to install them in the application you want to try them in.
+Just add them to the `composer.json` as you would normally do e.g. add `"yiisoft/yii2-redis": "*"` to the
+`require` section of the basic app.
+Running `./build/build app/link basic` will install the extension and its dependecies and create
+a symlink to `extensions/redis` so you are not working the composer vendor dir but the yii2 repo directly.
+