Created git_config/ for recommended settings

Initial version of directory only contains one file
  - git_commit_template.txt: contains template for commit log using Alistair's
                             recommendation for best practices (one-line
                             summary and detailed explanation)

To use, run the following from CVMix root directory:

$ git config commit.template git_config/git_commit_template.txt
Added comment about 79 character per line max

To be consistent with the best-practices in the Fortran code, the git commit
log should also have a max of 79 characters per line