Add an FAQ

Add an FAQ to the documentation. The first entry (and the only one so
far) is "Can bugarrior support <some issue tracking system>?"

bugwarrior/docs/faq.rst

@@ -0,0 +1,15 @@
+FAQ
+===
+
+Can bugarrior support <some issue tracking system>?
+---------------------------------------------------
+
+Sure! But our general rule here is that we won't write a backend for a service
+unless we use it personally, otherwise it's hard to be sure that it really
+works.
+
+We also try to rely on people to become maintainers of the different backend
+plugins they use so that they don't suffer bit rot over time.
+
+In summary, we need someone who 1) uses <some issue tracking system> and 2) can
+develop the plugin.  Could it be you? :)

bugwarrior/docs/index.rst

@@ -40,6 +40,7 @@ Contents
    services
    configuration
    contributing
+   faq
 
 
 Indices and tables