Add contribution guidelines

[jmayntzhusen]

With rising interest in UmbPack we are of course interested in having more people contribute. Contribution guidelines that give a quick overview of the codebase and how you can test things would be nice to make it easier for newcomers to dive in!

Should cover things like:

• Building the tool locally and testing the init and pack commands from the source
• Testing the push command with a local version of Our
• Overview of the Our apis UmbPack pushes to and what is possible there

@mattbrailsford anything you had trouble figuring out when you made PR's in the past you'd have loved to be documented somewhere? 🙂 @nathanwoulfe, likewise if you hit a wall with something related to contributing to UmbPack please add it here so we can get it documented!

[mattbrailsford]

I guess the difficult thing is testing it without having a package to deploy somewhere. Maybe not so much documentation, but maybe we need a mode where it would perform all the tasks, including maybe hitting the APIs but it says it's in test mode so that it can verify everything runs successfully and nothing is actually persisted. Maybe in test mode it can write a report of what it thinks would happen if it ran.

I really didn't want to have to deploy a local version of Our just to see if it works.

[jmayntzhusen]

Hmm a dry-run feature could be really nice! A bit outside the scope of what I had intended with this issue, but I like it!

[mattbrailsford]

@jmayntzhusen agreed it's out of scope of this issue, just you asking made me think of it 😁