Better docs to help onboard new contributors

[mkurz]

Probably https://www.playframework.com/documentation/2.8.x/BuildingFromSource isn't doing the job to get people started, we should set up a more detail howto with step by step guides. Also not sure if the referenced page isn't even up to date.
/cc @eloots

[cleliofs]

Good point @mkurz I am willing to join the Community, but I am a bit "lost" on how to start and get involved 👍 Ta

[mkurz]

@cleliofs I replied to your email you send to the play-team mailing list, thanks!

[mkurz]

Will be finally done in playframework/playframework#11549