Add note about CKAN directory and personal repo

In order to help developers set up a CKAN development environment, they need to clone from a personal repository. This will make it easier to open a pull request, for developers who are not part of the CKAN organizaiton.

Also, there was a bit of ambiguity as to where to run the `pip install -e git+CKAN-repo` command. The command should be run from within `/usr/lib/ckan/default` so that subsequent steps work as expected.

doc/maintaining/installing/install-from-source.rst

@@ -105,6 +105,13 @@ b. Install the recommended ``setuptools`` version:
        pip install setuptools==\ |min_setuptools_version|
 
 c. Install the CKAN source code into your virtualenv.
+   .. important::
+       For the following commands, make sure you are in your CKAN default directory. E.g.
+
+      .. parsed-literal::
+      
+         cd /usr/lib/ckan/default/
+   
    To install the latest stable release of CKAN (CKAN |latest_release_version|),
    run:
 
@@ -120,6 +127,15 @@ c. Install the CKAN source code into your virtualenv.
 
        pip install -e 'git+\ |git_url|\#egg=ckan'
 
+   .. tip::
+
+      If you would like to work submit a pull request with your changes, be sure you are working from a cloned repository.
+      Use your personal repository URL instead of the CKAN repository. E.g.
+
+      .. parsed-literal::
+         
+         pip install -e 'git=https://github.com/{your-username}/ckan.git#egg=ckan'
+   
    .. warning::
 
       The development version may contain bugs and should not be used for