Move examples from package doc to README.md with package decl and
imports to ensure it's compilable.
Move status of the package from package doc to README.md.
Add core concepts of MCP with example code snippets and testing
recommendations.
Change-Id: I5bf5000b922fa3942aba922713b12d0347295811
Reviewed-on: https://go-review.googlesource.com/c/tools/+/670316
Reviewed-by: Sam Thanawalla <samthanawalla@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
