docs: add a scripts/kernel-doc symbolic link

Some folks evidently have muscle memory expecting kernel-doc to be under
scripts/.  Now that we have moved it to tools/docs, leave behind a symbolic
link to reduce the global profanity count.

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

diff --git a/scripts/kernel-doc b/scripts/kernel-doc
new file mode 120000 (symlink)
index 0000000..9cc1459
--- /dev/null
+++ b/scripts/kernel-doc
@@ -0,0 +1 @@
+../tools/docs/kernel-doc
\ No newline at end of file