Corrected name and location of MRbrain.tar.gz

The link to MRbrain.tar.gz is dead. I also updated the correct name of the .gz archive.
 Corrected name and location of MRbrain.tar.gz 

The link to MRbrain.tar.gz is dead. I also updated the correct name of the .gz archive.
 Corrected name and location of MRbrain.tar.gz 

The link to MRbrain.tar.gz is dead. I also updated the correct name of the .gz archive.
 Corrected name and location of MRbrain.tar.gz 

The link to MRbrain.tar.gz is dead. I also updated the correct name of the .gz archive.
Merge pull request #152 from paulmueller/patch-1

Example mri.py: Corrected name and location of MRbrain.tar.gz