Tweak installation instructions in README

Author: jamiesnape

README.md

@@ -28,10 +28,15 @@ interface with existing workflows.
 ```
 git clone https://github.com/midasplatform/Midas.git midas
 cd midas
+chmod a+w core/configs/ data/ log/ tmp/
 curl -sS https://getcomposer.org/installer | php
 php composer.phar install
 ```
 
+Full installation documentation is available at
+
+<https://midas-server.readthedocs.org/>
+
 ## License ##
 
 Midas Server is licensed under the Apache License, Version 2.0.