Add yum as a linux package manager
Update to latest msysgit
Add details of nano for windows users
Removed editorializing of editor
Point msysgit link to main page rather than hardcoding download
Update R install details
Merge remote-tracking branch 'gdevenyi/improvesetup'

Merge Gabriel's pull request which among other things un-pins the
msysGit version [1].  We've had some problems with previous versions:

* Something about email prompting with 1.8.4 [2].
* "fatal: could not read..." errors on https:// clones with
  1.8.5.2-preview20131230 [3,4].

but Gabriel tested v1.9.0 and didn't see an email prompt [5] and Git
v1.9.0 fixed the HTTPS issue [6]:

> Fixed regression with interactive password prompt for remotes using
> the HTTPS protocol (issue msysgit/msysgit#111).

So until we find more problems, we're back to floating msysGit :).

[1]: https://github.com/swcarpentry/bc/pull/485
[2]: https://github.com/swcarpentry/bc/wiki/Configuration-Problems-and-Solutions#bash
[3]: https://github.com/swcarpentry/bc/commit/fae9c74704b96de1e82a72533837612fb4a24877
[4]: https://github.com/swcarpentry/bc/issues/234#issuecomment-32764692
[5]: https://github.com/swcarpentry/bc/pull/485#issuecomment-42759353
[6]: https://github.com/msysgit/msysgit/releases/tag/Git-1.9.0-preview20140217

* gdevenyi/improvesetup:
  Update R install details
  Point msysgit link to main page rather than hardcoding download
  Removed editorializing of editor
  Add details of nano for windows users
  Update to latest msysgit
  Add yum as a linux package manager