[SoM] Documentation

[spouliot]

This includes

• Creating a branch in xamarin-docs-pr for the 1st preview
• Setting up the structure
• Step-by-step instructions on a happy (to be defined) project
• Documenting limitations / known issues
• Documenting error codes

[bradumbaugh]

@stephen-hawley Do you have a list/descriptions of errors/error codes produced by Swift-O-Matic?

[stephen-hawley]

Not yet. I have a TODO to comb through all the errors and (1) make them delightful and (2) put them in "standard format" with error codes.

[bradumbaugh]

Documentation branch / basic structure: https://review.docs.microsoft.com/en-us/xamarin/tools/swift-o-matic/?branch=brumbaug-swift