tools: include script to help generate CHANGELOG

Initial implementation to generate CHANGELOG. This is a
very rough tool, but I know others have updates to this
script so want to get this initial tool submitted.

Change-Id: I343098dbe82b451e8b4f7f5ddb6ac524b3c620c6
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/256579
Trust: Suzy Mueller <[email protected]>
Run-TryBot: Suzy Mueller <[email protected]>
TryBot-Result: kokoro <[email protected]>
Reviewed-by: Rebecca Stambler <[email protected]>

Author: suzmue

go.mod

@@ -1,3 +1,5 @@
 module github.com/golang/vscode-go
 
 go 1.16
+
+require golang.org/x/build v0.0.0-20210617174213-df58bbac082b