Documentation: Move documentation license to main menu

The "Getting started" section is not an appropriate place for the
documentation license. It should rather be listed in the main menu.
Thus, move it there.

Change-Id: I8bfc4f52da8a93d78a62e3a68fd6f1dc8ae4d335
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/62767
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>

Documentation/getting_started/index.md

@@ -4,6 +4,5 @@
 * [Build System](build_system.md)
 * [Submodules](submodules.md)
 * [Kconfig](kconfig.md)
-* [Documentation License](license.md)
 * [Writing Documentation](writing_documentation.md)
 * [Setting up GPIOs](gpio.md)

Documentation/index.md

@@ -190,3 +190,4 @@ Contents:
 * [Utilities](util.md)
 * [coreboot infrastructure](infrastructure/index.md)
 * [Release notes](releases/index.md)
+* [Documentation License](documentation_license.md)