Clarify Mac OS X experience.

Signed-off-by: Mary Anthony <moxieandmore@gmail.com>

docs/sources/contributing/devenvironment.md

@@ -40,22 +40,24 @@ with the name of branch or revision number.
 
 ## Build the Environment
 
-This following command will build a development environment using the
-Dockerfile in the current directory. Essentially, it will install all
+This following command builds a development environment using the
+Dockerfile in the current directory. Essentially, it installs all
 the build and runtime dependencies necessary to build and test Docker.
-This command will take some time to complete when you first execute it.
+Your first build will take some time to complete. On Linux systems:
 
     $ sudo make build
+    
+On Mac OS X, from within the `boot2docker` shell:
+
+    $ make build
+
+> **Note**:
+> On Mac OS X, **do not** build Docker make targets such as `build`, `binary`, and `test`
+> under root (sudo). 
 
 If the build is successful, congratulations! You have produced a clean
 build of docker, neatly encapsulated in a standard build environment.
 
-> **Note**:
-> On Mac OS X, make targets such as `build`, `binary`, and `test`
-> must **not** be built under root. So, for example, instead of the above
-> command, issue:
-> 
->     $ make build
 
 ## Build the Docker Binary