Add instructions for how to get commit hash

.github/ISSUE_TEMPLATE.md

@@ -29,5 +29,5 @@ If you have access to the server log files, also copy them here.
 <!-- The version of your browser (when it is a client-side issue) -->
 **Browser:**
 
-<!-- The version of PrivateBin, if you use a unstable version paste the commit hash or the GitHub link to the commit here -->
+<!-- The version of PrivateBin, if you use a unstable version paste the commit hash or the GitHub link to the commit here (you can get it by running `git rev-parse HEAD`) -->
 **PrivateBin version:**