[documentation] new how-to to switch into branch, and add info about gitlab tokens

docs/source/installation/index.rst

@@ -104,6 +104,29 @@ The password is always ``password``.
 
 Now, read `Operations` below.
 
+Prepare for development
+***********************
+
+Add a Gitlab token to ensure that you get always the source code:
+
+1. generate a gitlab token there: https://gitlab.com/oauth/token
+2. run this command (in php container, at the app's root): :code:`composer config gitlab-token.gitlab.com <your token>`
+
+The auth token should appears now in the directory :code:`.composer`:
+
+... code-block: bash
+
+   $ cat .composer/auth.json
+   {
+       "gitlab-token": {
+           "gitlab.com": "<your token>"
+       }
+   }
+
+
+See also "how to switch branch and get new dependencies".
+
+
 Operations
 **********
 
@@ -211,6 +234,25 @@ How to run webpack interactively
 
 Executing :code:`bash docker-node.sh` will open a terminal in a node container, with volumes mounted.
 
+How to switch the branch for chill-bundles, and get new dependencies
+====================================================================
+
+During development, you will switch to new branches for chill-bundles. As long as the dependencies are equals, this does not cause any problem. But sometimes, a new branch introduces a new dependency, and you must download it.
+
+In order to do that without pain, use those steps:
+
+0. Ensuire you have a token, set
+1. at the app's root, update the `composer.json` to your current branch:
+
+.. code-block:: json
+   {
+      "require": {
+          "chill-bundles": "dev-<my-branch>@dev"
+   }
+```
+
+2. mount into the php container, and run `composer update`
+
 Build the documentation API
 ===========================