Correct description and release note

CMakeFilters.cmake

@@ -92,7 +92,7 @@ endif ()
 if (HDF5_ENABLE_ZLIB_SUPPORT)
   if (NOT H5_ZLIB_HEADER)
     if (NOT ZLIB_USE_EXTERNAL)
-      option (HDF5_MODULE_MODE_ZLIB "Find the default system ZLIB in module mode" ON)
+      option (HDF5_MODULE_MODE_ZLIB "Prefer module mode to find ZLIB" ON)
       mark_as_advanced (HDF5_MODULE_MODE_ZLIB)
       if (HDF5_USE_ZLIB_NG)
         set (HDF5_MODULE_MODE_ZLIB OFF CACHE BOOL "" FORCE)

release_docs/INSTALL_CMake.txt

@@ -877,7 +877,7 @@ if (BUILD_TESTING)
 HDF5_ALLOW_EXTERNAL_SUPPORT "Allow External Library Building (NO GIT TGZ)"       "NO"
 HDF5_ENABLE_PLUGIN_SUPPORT  "Enable PLUGIN Filters"                              OFF
 HDF5_ENABLE_SZIP_SUPPORT    "Use SZip Filter"                                    OFF
-HDF5_MODULE_MODE_ZLIB       "Find the default system ZLIB in module mode"        ON
+HDF5_MODULE_MODE_ZLIB       ""Prefer module mode to find ZLIB"                   ON
 HDF5_ENABLE_ZLIB_SUPPORT    "Enable Zlib Filters"                                OFF
 
 if (HDF5_USE_ZLIB_NG)

release_docs/RELEASE.txt

@@ -575,9 +575,11 @@ Bug Fixes since HDF5-2.0.0 release
     - When using a system installed zlib library, the shared library is expected to
       be found in the system library path.
 
-      Setting the HDF5_MODULE_MODE_ZLIB option to OFF, the system installed zlib,
-      or an alternate installed zlib library, is expected to have a correct
-      zlib-config.cmake file.
+      Setting the HDF5_MODULE_MODE_ZLIB option to OFF will force find_package to
+      use config mode first, an installed zlib, or an alternate installed zlib
+      library, is expected to have a correct zlib-config.cmake file.
+      Current zlib installs usually do not have a zlib-config.cmake file, so the
+      option is set to ON by default.
 
     - Use pre-installed libaec compression library