Update README.md

Mention alias as an alternative to symbolic links.
Potentially a better solution as it doesn't require root access.
Potentially not because not everybody uses bash.
add markdown syntax highlighting to themes

based on http://www.bram.us/2013/02/08/sublime-text-markdown-syntax-highlighting/
Merge pull request #13 from ujpandey/master

Update README.md to include adding an alias as an alternative to creating a symbolic link.
Merge pull request #15 from nicodeceulaer/markdown_syntax

add markdown syntax highlighting to themes
Merge branch 'master' of https://github.com/mhartl/rails_tutorial_sublime_text