This is an example repo to get you started. The main points of interest are

• The .platform directory, and the two files therein - routes.yaml and services.yaml. These files define project wide webserver configuration and your MySQL database, respectively.
• The .platform.app.yaml file in the root of this project. This is the application definition file, and sets up all the parameters needed for Moodle to run on Platform.sh
• The public/config.php file, where the Platform.sh config-reader Composer package is autoloaded, and the database connection info is set.

• The entire download was placed into the public directory, rather than being in the root of the repo.
• The composer.json and composer.lock files were moved up a directory into the root of the repo. This only appears to load behat for dev (by default), but this repo also loads the config-reader Composer package referenced above.
• public/config.php was modified in the following places
  • Lines 3-4 to autoload platformsh-config-reader package
  • Lines 72-99 to set DB connection info. You shouldn't need to touch this to get started.
  • Lines 129-132 to set the moodledata directory if in a PSH environment.
  • Line 134 to set the default homepage. This cured a bizarre redirect loop that nothing else would, short of putting on the deep diving gear. See https://moodle.org/mod/forum/discuss.php?d=227536 for more.