Add tag command, update guide, add PR templates (#2679)

scripts/tag-release.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+if [[ ${git branch --show-current} =~ ^release/v ]]
+then
+  VERSION_STRING=$(cat package.json | jq '.version' -r | xargs printf "v%s")
+  git tag ${VERSION_STRING}
+  git push ${GIT_REMOTE:-origin} ${VERSION_STRING}
+else
+  echo "You must be in a release branch"
+fi