Merge branch 'sb/submodule-config-doc-drop-path' into maint

The "submodule.<name>.path" stored in .gitmodules is never copied to .git/config and such a key in .git/config has no meaning, but the documentation described it and submodule.<name>.url next to each other as if both belong to .git/config. This has been fixed. * sb/submodule-config-doc-drop-path: documentation: improve submodule.<name>.{url, path} description