Update contributing.md
mcs instead of gcs

fix #43
Merge pull request #44 from txdv/patch-1

mcs instead of gcs
Added SUSE Factory repo link
Use mcs instead of gmcs.
Merge pull request #46 from mcgwiz/gh-pages

Use mcs instead of gmcs
Fix a minor typo.
Added some clarity to the download page regarding MRE vs. MDK

Fixes #42
Updated github-pages gem to v28
Merge pull request #47 from joshpeterson/patch-1

Fix a minor typo.
Merge pull request #45 from nilsh/gh-pages

Added SUSE Factory repo link
fixed typo
Fixed a small inadvertent change done in 2fd9584683c6afd7330c93195cafac0410939d5f.
Fixed a couple of code formatting problems on the "Embedding Mono" page
Get rid of separate distro pages in favor of the Linux install guide
Emphasize running commands in a root shell as some people tripped over this
Added a few more redirects for moonlight that showed up in GA
Added alt tags for images that had none

They are not necessarily descriptive ones, but that can be done later.
Fixed internal links that were pointing to an invalid url
Fixed a few invalid urls