message: Add alternate git url in contributors guide
diff: @@ -16,6 +16,13 @@ To setup your local repository for development:
  ```
  [chuck@hal9000 Code]$ mkdir adios
  [chuck@hal9000 Code]$ cd adios
  +#
  +# If you don't have ssh access setup to your github repository then you will
  +# need to clone your fork from
  +# https://github.com/<your-GitHub-username-here>/adios2.git
  +# instead of
  +# git@github.com:<your-GitHub-username-here>/adios2.git
  +#
  [chuck@hal9000 adios]$ git clone git@github.com:<your-GitHub-username-here>/adios2.git source
  Cloning into 'source'...
  remote: Counting objects: 4535, done.
  