docs: process: Add an example for creating a fixes tag

To make it a little clearer how to create a fixes tag,
add an example based on the preceeding gitconfig setup.
Signed-off-by: Tom Rix <trix@redhat.com>
Link: https://lore.kernel.org/r/20200710200115.21176-1-trix@redhat.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/process/submitting-patches.rst

@@ -196,6 +196,11 @@ outputting the above style in the ``git log`` or ``git show`` commands::
 	[pretty]
 		fixes = Fixes: %h (\"%s\")
 
+An example call::
+
+	$ git log -1 --pretty=fixes 54a4f0239f2e
+	Fixes: 54a4f0239f2e ("KVM: MMU: make kvm_mmu_zap_page() return the number of pages it actually freed")
+
 .. _split_changes:
 
 3) Separate your changes