ENH: Added documentation about XXX_FIND_COMPONENTS for FIND_PACKAGE.

Modules/readme.txt

@@ -71,8 +71,9 @@ XXX_FIND_REQUIRED to true before loading the FindXXX.cmake module.  If
 this variable is set the module should issue a FATAL_ERROR if the
 package cannot be found.  For each package-specific component, say
 YYY, listed after the REQUIRED option a variable XXX_FIND_REQUIRED_YYY
-to true.  This can be used by the FindXXX.cmake module to determine
-which sub-components of the package must be found.  If neither the
-QUIET nor REQUIRED options are given then the FindXXX.cmake module
-should look for the package and complain without error if the module
-is not found.
+to true.  The set of components listed will also be specified in a
+XXX_FIND_COMPONENTS variable.  This can be used by the FindXXX.cmake
+module to determine which sub-components of the package must be found.
+If neither the QUIET nor REQUIRED options are given then the
+FindXXX.cmake module should look for the package and complain without
+error if the module is not found.