Update minimum bash version

Clarify our position on bash and other shells.

Change-Id: I30e801afa03f8d7235556b0933d0205a30310899
diff --git a/doc/source/faq.rst b/doc/source/faq.rst
index fd9c736..a449f49 100644
--- a/doc/source/faq.rst
+++ b/doc/source/faq.rst
@@ -70,6 +70,18 @@
 Q: Are there any differences between Ubuntu and Fedora support?
     A: Neutron is not fully supported prior to Fedora 18 due lack of
     OpenVSwitch packages.
+Q: Why can't I use another shell?
+    A: DevStack now uses some specific bash-ism that require Bash 4, such
+    as associative arrays. Simple compatibility patches have been accepted
+    in the past when they are not complex, at this point no additional
+    compatibility patches will be considered except for shells matching
+    the array functionality as it is very ingrained in the repo and project
+    management.
+Q: But, but, can't I test on OS/X?
+   A: Yes, even you, core developer who complained about this, needs to
+   install bash 4 via homebrew to keep running tests on OS/X.  Get a Real
+   Operating System.   (For most of you who don't know, I am refering to
+   myself.)
 
 Operation and Configuration
 ===========================