Help: Clarify load_cache documentation of first parameter

The first parameter is the path to the *directory* containing the
`CMakeCache.txt` file, not the file itself.

Help/command/load_cache.rst

@@ -5,7 +5,7 @@ Load in the values from another project's CMake cache.
 
 .. code-block:: cmake
 
-  load_cache(pathToCacheFile READ_WITH_PREFIX prefix entry1...)
+  load_cache(pathToBuildDirectory READ_WITH_PREFIX prefix entry1...)
 
 Reads the cache and store the requested entries in variables with their
 name prefixed with the given prefix.  This only reads the values, and
@@ -13,7 +13,7 @@ does not create entries in the local project's cache.
 
 .. code-block:: cmake
 
-  load_cache(pathToCacheFile [EXCLUDE entry1...]
+  load_cache(pathToBuildDirectory [EXCLUDE entry1...]
              [INCLUDE_INTERNALS entry1...])
 
 Loads in the values from another cache and store them in the local