nginx: update Passenger caveats.

They now explicitly mention the fact that passenger_root and passenger_ruby
must be specified in the 'http' context. See
http://stackoverflow.com/questions/24220300/configuring-passenger-with-ngenix
for a user who didn't get this and did it wrong.

Closes Homebrew#30155.

Signed-off-by: Jack Nagel <[email protected]>

Library/Formula/nginx.rb

@@ -121,7 +121,7 @@ def post_install
 
   def passenger_caveats; <<-EOS.undent
 
-    To activate Phusion Passenger, add this to #{etc}/nginx/nginx.conf:
+    To activate Phusion Passenger, add this to #{etc}/nginx/nginx.conf, inside the 'http' context:
       passenger_root #{HOMEBREW_PREFIX}/opt/passenger/libexec/lib/phusion_passenger/locations.ini
       passenger_ruby /usr/bin/ruby
     EOS