Don't blindly include [BUG] on rakudobugs

Give the submitters a few choices.

README.md

@@ -93,15 +93,22 @@ For questions about MoarVM, you can join #moarvm on freenode.
 
 ## Reporting bugs
 
-Bug reports should be sent to "rakudobug@perl.org" with the moniker
-[BUG]\(including the brackets) at the start of the subject so that it
-gets appropriately tagged in [the RT system](https://rt.perl.org/rt3/).
+Bug reports should be sent to "rakudobug@perl.org", which will
+automatically create a ticket in 
+[the RT system](https://rt.perl.org/rt3/).
 Please include or attach any sample source code that exhibits the bug,
 and include either the release name/date or the git commit identifier.
 You find that information in the output from `perl6 --version` (or in
 the first line of `git log`, if Rakudo fails to build). There's no need
 to cc: the perl6-compiler mailing list, as the RT system will handle
-this on its own.
+this on its own. Please start your subject with one (or more) of the
+following text, including the brackets:
+
+* [BUG]  - this is an actual bug
+* [LTA]  - a "Less Than Awesome" diagnostic or warning is being generated
+* [JVM]  - issue only occurs on the JVM
+* [PERF] - any performance related issue
+* [UNI]  - related to unicode support
 
 If you find a bug in MoarVM or NQP, you can either discuss it on the IRC
 and have it reported for you, or you can submit an issue to the issue