Update file names

Author: WeiqunZhang

Docs/sphinx_documentation/source/index.rst

@@ -71,8 +71,8 @@ Documentation on migration from BoxLib is available in the AMReX repository at D
    :caption: API
 
 The copyright notice of AMReX is included in the AMReX home directory
-as README.txt.
+as README.md.
 Your use of this software is under the 3-clause BSD license -- the license agreement is included in the
-AMReX home directory as license.txt.
+AMReX home directory as LICENSE.
 
 For a pdf version of this documentation, click :download:`here <amrex.pdf>`.