#2 #3 Documentation for new features in Drupal pipelines

docs/gitlab/drupal/index.md

@@ -182,11 +182,19 @@ you have to write the scripts for those two tasks yourselves.
 
 #### Variables
 
-- `COMPOSE_PROJECT_NAME`
-- `ENVIRONMENT_NAME`
-- `THEME_CSS_PATH`
+- `COMPOSE_PROJECT_NAME`: a string only unique project name which will be used
+  to identify caches and Docker containers.
+- `ENVIRONMENT_NAME`: the environment name for the GitLab UI.
+- `THEME_CSS_PATH`: the relative path to the theme's css path where the
+  generated artefact can be found.
+- `PHP_MAJOR_VERSION`: the major PHP version, defaults to 7.
+- `PHP_MINOR_VERSION`: the minor PHP version, default to 4.
 - `COMPOSER_DOWNGRADE`: by default, composer 2 is being used. To use composer 1
   instead, set this variable to 1.
+- `INITIAL_INSTALL`: if set to `yes`, the initial Drupal site installation gets
+  triggered and all DB and test tasks will be skipped.
+- `PULL_DB`: if set to `yes`, the download of a fresh database dump will be
+  forced, regardless of any other conditions.
 - `DISABLE_CI_TESTS`: if this variable is set to any value, the tasks in the
   test stage will be skipped. This is useful e.g. in a development environment
   where you push and run pipelines often but don't want to run the tests every
@@ -302,6 +310,20 @@ site in your inventory.
 
 This chapter is incomplete so far and needs more attention.
 
+### Initial installation of a Drupal site
+
+This pipeline covers both, the initial installation and later updates of a
+Drupal site. The latter is the default, because it happens regularely whereas
+the initial installation only happens once.
+
+Therefore, if you run the pipeline the first time to initially install the
+Drupal site, either add `[INITIAL_INSTALL]` to your commit message or define
+the variable `INITIAL_INSTALL` with the value `yes` when triggering the
+pipeline from the GitLab UI.
+
+When either of these conditions apply, no database will be downloaded, imported
+or updated and all tests will be skipped.
+
 ### Handling of the database
 
 To build and test your Drupal site prior to deployment, a database with content