manual: github commits should be specified in full

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Acked-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

docs/manual/adding-packages-tips.txt

@@ -44,14 +44,13 @@ However, it is possible to download tarballs directly from the repository
 on github.
 
 ------------------------
-FOO_VERSION = v1.0 # tag or (abbreviated) commit ID
+FOO_VERSION = v1.0 # tag or full commit ID
 FOO_SITE = http://github.com/<user>/<package>/tarball/$(FOO_VERSION)
 ------------------------
 
 .Notes
 - The FOO_VERSION can either be a tag or a commit ID.
 - The tarball name generated by github matches the default one from
-  Buildroot (e.g.: +foo-1234567.tar.gz+),
+  Buildroot (e.g.: +foo-f6fb6654af62045239caed5950bc6c7971965e60.tar.gz+),
   so it is not necessary to specify it in the +.mk+ file.
-- When using a commit ID as version, usually the first 7 characters of
-  the SHA1 are enough.
+- When using a commit ID as version, you should use the full 40 hex characters.