Simple grammar and update to link (#3415)

CONTRIBUTING.md

@@ -85,7 +85,7 @@ Before you start changing the docs, you'll want to
 [fork the Superset project on Github](https://help.github.com/articles/fork-a-repo/).
 Once that new repository has been created, clone it on your local machine:
 
-    git clone git@github.com:your_username/superset.git
+    git clone git@github.com:your_username/incubator-superset.git
 
 At this point, you may also want to create a
 [Python virtual environment](http://docs.python-guide.org/en/latest/dev/virtualenvs/)
@@ -97,7 +97,7 @@ to manage the Python packages you're about to install:
 Finally, to make changes to the rst files and build the docs using Sphinx, 
 you'll need to install a handful of dependencies from the repo you cloned:
 
-    cd superset
+    cd incubator-superset
     pip install -r dev-reqs-for-docs.txt
 
 To get the feel for how to edit and build the docs, let's edit a file, build

docs/security.rst

@@ -36,7 +36,7 @@ own. Alpha users can add and alter data sources.
 Gamma
 """""
 Gamma have limited access. They can only consume data coming from data sources
-they have been giving access to through another complementary role.
+they have been given access to through another complementary role.
 They only have access to view the slices and
 dashboards made from data sources that they have access to. Currently Gamma
 users are not able to alter or add data sources. We assume that they are