docs: admin-guide: Sort the "unordered guides" to avoid merge conflicts

Since the "unordered guides" linked in admin-guide/index.rst are not
supposed to be in any particular order, let's sort them alphabetically
to avoid the risk of merge conflicts by spreading newly added lines more
evenly.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>