note "Pandas install from source error" in documentation when using mingw
Installing on Windows with MinGW installed. 

Pandas Version: Installing from source
NumPy Version : `1.7.1`

After running `setup.py install`  I get this error: 

```
cc1.exe: error: unrecognized command line option '-mno-cygwin'
error: command 'gcc' failed with exit status 1 
```

I believe I've installed MinGW correctly. Is this a problem with Pandas or MinGW?  

Terminal output:

```
C:\Python27\Lib\site-packages\pandas>setup.py install
running install
running bdist_egg
running egg_info
writing requirements to pandas.egg-info\requires.txt
writing pandas.egg-info\PKG-INFO
writing top-level names to pandas.egg-info\top_level.txt
writing dependency_links to pandas.egg-info\dependency_links.txt
reading manifest file 'pandas.egg-info\SOURCES.txt'
reading manifest template 'MANIFEST.in'
warning: no files found matching 'TODO.rst'
warning: no files found matching 'setupegg.py'
no previously-included directories found matching 'doc\build'
warning: no previously-included files matching '*.so' found anywhere in distribution
warning: no previously-included files matching '*.pyd' found anywhere in distribution
warning: no previously-included files matching '*.pyc' found anywhere in distribution
warning: no previously-included files matching '.DS_Store' found anywhere in distribution
warning: no previously-included files matching '*.png' found anywhere in distribution
writing manifest file 'pandas.egg-info\SOURCES.txt'
installing library code to build\bdist.win-amd64\egg
running install_lib
running build_py
copying pandas\version.py -> build\lib.win-amd64-2.7\pandas
running build_ext
skipping 'pandas\index.c' Cython extension (up-to-date)
building 'pandas.index' extension
C:\MinGW\bin\gcc.exe -mno-cygwin -mdll -O -Wall -Ipandas/src/klib -Ipandas/src -
IC:\Python27\lib\site-packages\numpy\core\include -IC:\Python27\include -IC:\Pyt
hon27\PC -c pandas\index.c -o build\temp.win-amd64-2.7\Release\pandas\index.o
cc1.exe: error: unrecognized command line option '-mno-cygwin'
error: command 'gcc' failed with exit status 1
```
