CODING_STYLE: explicitly call out label indentation

Since the behavior of "diff -p" to use an unindented label as context
identifier often makes it harder to review patches, make explicit the
requirement for labels to be indented.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>

CODING_STYLE

@@ -47,6 +47,10 @@ void fun(void)
     }
 }
 
+Due to the behavior of GNU diffutils "diff -p", labels should be
+indented by at least one blank.  Non-case labels inside switch() bodies
+are preferred to be indented the same as the block's case labels.
+
 White space
 -----------