Update Readme with steps to contribute new Tips

[prnadago]

Rough steps:

• fork the repo
• add tip in markdown file to Tips folder
• add tip entry to appropriate groups json. Create new json if new group.
• update EmbeddedTipProvider.cs if creating a new group
• submit PR

[justcla]

I made a start. But I keep making typos. Please go ahead and improve it (in a new branch). Thanks!