doc: extend notes about contributing; add issue template

.github/CONTRIBUTING.md

@@ -0,0 +1,58 @@
+# Contributing
+
+Before you start working on a PR, contact us via IRC in #froxlor on Freenode or
+the forum at https://forum.froxlor.org to get a clue whether someone else isn't
+already working on it or if we don't want to invest the effort in favour of
+working on Froxlor 2.0.
+Of course, bug fixes are always welcome.
+However, at this stage of the 0.9.x branch, we are not looking for new
+features or refactoring, especially not the kind which requires changes to a
+lot of files.
+Currently, we are working on a complete re-write, which, at this point in
+time, is not yet public to keep delays due to discussions about internal
+details to a minimum.
+
+
+
+
+## Checklist
+
+General rules for PRs are:
+* Please save us all some trouble and unnecessary round-trips by _testing_ your
+changes.
+
+* Re-write your commit history to provide a CLEAN history!
+
+	* i.e. do not provide PRs which contain a commit that changes something,
+	the next changes it back, a third one changes it again, only a little
+	differently...
+
+
+Thanks!
+
+
+
+
+### Webserver changes
+If you make changes to the functionality of webserver configuration, please
+make sure your implementation covers both apache **and** nginx.
+
+
+
+
+### l10n
+
+If you add new language strings, please make sure you add the english fallback
+strings in
+
+* `lng/english.lng.php`
+* `install/lng/english.lng.php` (if applicable)
+
+
+
+
+### New settings
+If you add new settings, please make sure you add the default values to
+
+* `install/froxlor.sql`
+* handle the update (see `install/updates/froxlor/0.9/update_0.9.inc.php`)