[tcgc] add go sections in DPG how to docs

[iscai-msft]

Clear and concise description of the problem

We have good coverage for the 4 core languages in our DPG how to docs. Now that Go is very mature in its development, they should go ahead and add sections for their emitters to the docs listed in the above link

Checklist

• Follow our Code of Conduct
• Check that this issue is about the Azure libraries for typespec. For feature request in the typespec language or core libraries file it in the TypeSpec repo
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.