[Tgcmgroup] updated TGCM documentation

[Ben Foster]

Hi Tgcmgroup:

The TGCM User's Guide and draft Model Description have been
updated. Please see the Documentation section of the main TGCM
website http://www.hao.ucar.edu/modeling/tgcm for both html and pdf.

In addition, a new document "TIEGCM Code Structure Flowchart"
is available in the Documentation section of the TGCM Download page:
http://www.hao.ucar.edu/modeling/tgcm/download.php (email registration
required).

--Ben