Add example CGI script

This gives an example of how to easily use hgweb via CGI

hgweb.cgi

@@ -0,0 +1,10 b''
+#!/usr/bin/python
+#
+# An example CGI script to use hgweb, edit as necessary
+
+import cgitb, os, sys
+# sys.path.insert(0, "/path/to/python/lib") # if not a system-wide install
+from mercurial import hgweb
+
+h = hgweb.hgweb("/path/to/repo", "repository name")
+h.run()