load_cache: Mention script mode support (-P)

When using the relevant load_cache(READ_WITH_PREFIX) signature, it also
works in script mode (cmake -P ...), unlike the 2nd obsolete signature.

Help/command/load_cache.rst

@@ -21,6 +21,8 @@ This command has two signatures.  The recommended signature is:
     For each cache ``<entry>``, a local variable is created using the specified
     ``<prefix>`` followed by the entry name.
 
+  This signature can be also used in :option:`cmake -P` script mode.
+
 The following signature of this command is strongly discouraged, but it is
 provided for backward compatibility:
 
@@ -42,6 +44,9 @@ provided for backward compatibility:
     This option can be used to provide a list of internal cache entries to
     include in addition to the non-internal cache entries.
 
+  This signature can be used only in CMake projects.  Script mode is not
+  supported.
+
 Examples
 ^^^^^^^^
 

Help/manual/cmake-commands.7.rst

@@ -51,6 +51,7 @@ These commands are always available.
    /command/include
    /command/include_guard
    /command/list
+   /command/load_cache
    /command/macro
    /command/mark_as_advanced
    /command/math
@@ -105,7 +106,6 @@ These commands are available only in CMake projects.
    /command/install
    /command/link_directories
    /command/link_libraries
-   /command/load_cache
    /command/project
    /command/remove_definitions
    /command/set_source_files_properties