ENH: Installing readme.txt in Modules directory to be consistent with windows.

Modules/CMakeLists.txt

@@ -4,4 +4,4 @@ INSTALL_FILES(${CMAKE_DATA_DIR}/Modules .*\\.cmake$)
 INSTALL_FILES(${CMAKE_DATA_DIR}/Modules .*\\.cxx$)
 INSTALL_FILES(${CMAKE_DATA_DIR}/Modules .*\\.in$)
 INSTALL_FILES(${CMAKE_DATA_DIR}/Modules .*\\.c$)
-
+INSTALL_FILES(${CMAKE_DATA_DIR}/Modules readme\\.txt$)