fix file name link

Author: wkliao

wiki/Documentation.html

@@ -35,7 +35,7 @@ <h2>Build PnetCDF Library</h2>
 </li><li>Several README files contain build recipes for specific platforms, including
 <ul><li><a href="https://github.com/Parallel-NetCDF/PnetCDF/blob/master/doc/README.CRAY.md">README.CRAY</a>
 </li><li><a href="https://github.com/Parallel-NetCDF/PnetCDF/blob/master/doc/README.Fujitsu.md">README.Fujitsu</a>
-</li><li><a href="https://github.com/Parallel-NetCDF/PnetCDF/blob/master/doc/README.IBM">README.IBM</a>
+</li><li><a href="https://github.com/Parallel-NetCDF/PnetCDF/blob/master/doc/README.IBM.md">README.IBM</a>
 </li><li><a href="https://github.com/Parallel-NetCDF/PnetCDF/blob/master/doc/README.INTEL.md">README.INTEL</a>
 </li><li><a href="https://github.com/Parallel-NetCDF/PnetCDF/blob/master/doc/README.K-Computer.md">README.K-Computer</a>
 </li><li><a href="https://github.com/Parallel-NetCDF/PnetCDF/blob/master/doc/README.LINUX.md">README.LINUX</a>