(maint) Ignore docs folder on package build

This adds the docs folder to the VSCode ignore file so that we do not
include it in the vsix package. This reduces the size of the package
from about ~13MB to ~1MB.

Author: jpogran

.vscodeignore

@@ -10,3 +10,4 @@ tmp/**
 logs/**
 sessions/**
 gulpfile.js
+docs