trivial: manual: fix typo formating --> formatting

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Acked-by: "Samuel Martin" <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

docs/manual/adding-packages-directory.txt

@@ -203,5 +203,5 @@ different way, using different infrastructures:
    CMake. We cover them through a xref:cmake-package-tutorial[tutorial]
    and xref:cmake-package-reference[reference].
 
-Further formating details: see xref:writing-rules-mk[the writing
+Further formatting details: see xref:writing-rules-mk[the writing
 rules].