Ensure extension-readme.md is present at package for packaging test (#1055)

extension-readme.md may not always be a static file. Any changes made to it will be done in generateNonCodeFiles.

Author: bryceitoc9

buildspec/packageTestVsix.yml

@@ -9,14 +9,15 @@ phases:
     install:
         runtime-versions:
             nodejs: 10
-            
+
     pre_build:
         commands:
             # --unsafe-perm is needed because we run as root
             - npm install --unsafe-perm
-            
+
     build:
         commands:
+            - npm run generateNonCodeFiles
             - cp ./extension-readme.md ./README.md
             - npm run package