Add Issue submission template (redirect to bugs.lede-project.org)

Signed-off-by: Ted Hess <thess@kitschensync.net>

.github/issue_template

@@ -0,0 +1,13 @@
+This repository is a mirror of our main repo at https://git.lede-project.org/sources.git
+It is for reference only and is not active for checkins or for reporting issues.
+
+All issues should be reported at: https://bugs.lede-project.org
+
+Please do not open any NEW issue here - we will be closing the Github issues
+capability in the near future.
+
+We will continue to accept Pull Requests here as described in the repo description.
+
+Close this now and click here: https://bugs.lede-project.org
+
+Thankyou for your co-operation.