Improve CONTRIBUTING wrt. tests

CONTRIBUTING.md

@@ -19,20 +19,19 @@ To make things easier on everyone, try to reproduce the issue with a minimal vim
 checkout of vim-perl.  Taking the time to help out with issues you have found makes things easier on all
 of us, and that's the whole reason this is an open project. =)
 
+Also, before you report something as a bug, please make sure you're using the latest version of
+vim-perl from Git.  If you're using an older version, chances are that you're stumbling on a bug that
+someone else has in the past.
+
 If you have read and understand these guidelines, add the text "I have read the guidelines" in your issue
 when you create it.
 
 # Helping Out
 
 If you would like to contribute to vim-perl, please be aware that we have a test suite which can
-be run using the `prove` command.  We also have a regression test suite in the `build-corpus.pl`
-and `verify-corpus.pl` scripts.  If you plan on making changes to vim-perl, please drop the sources
-for `Moose`, `Data::Printer`, and `Regexp::Debugger` under a directory named `corpus` under the
-Git root, and extract the archives.  Then run `build-corpus.pl`; this will take a few seconds.
-
-After you've made your changes, run the test suite via `prove`, as well as the regression tests
-via `verify-corpus.pl`.  The former tests a host of known situations for consistency, and the
-latter simply verifies that vim-perl still highlights and folds code the way it did when you
-ran `build-corpus.pl`.  Most fixes don't change highlighting, so `verify-corpus.pl` should print
-nothing.  If it does, open the file(s) printed and make sure that their highlighting still makes
-sense.
+be run using the `prove` command.  After you've made your changes, run the test suite via `prove`.
+The tests test a host of known situations for consistency, as well as verifies that vim-perl still
+highlights and folds code the way it does with the latest code on GitHub.  Most fixes don't change highlighting,
+so the regression test should pass.  If it fails, open the file(s) printed and make sure that their highlighting
+still makes sense.  If it does, note that in your pull request and a maintainer will update the regression corpus
+data when he/she merges it.