docs: document the new github helper function

[Thomas: splitted from Mischa original commit]

Signed-off-by: Mischa Jonker <mjonker@synopsys.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

docs/manual/adding-packages-generic.txt

@@ -230,7 +230,9 @@ information is (assuming the package name is +libfoo+) :
   URL or a local filesystem path. HTTP, FTP and SCP are supported URL
   types for retrieving package tarballs. Git, Subversion, Mercurial,
   and Bazaar are supported URL types for retrieving packages directly
-  from source code management systems. A filesystem path may be used
+  from source code management systems. There is a helper function to make
+  it easier to download source tarballs from github (refer to
+  xref:github-download-url[] for details). A filesystem path may be used
   to specify either a tarball or a directory containing the package
   source code. See +LIBFOO_SITE_METHOD+ below for more details on how
   retrieval works. +
@@ -244,7 +246,6 @@ information is (assuming the package name is +libfoo+) :
   Examples: +
     +LIBFOO_SITE=http://www.libfoosoftware.org/libfoo+ +
     +LIBFOO_SITE=http://svn.xiph.org/trunk/Tremor/+ +
-    +LIBFOO_SITE=git://github.com/kergoth/tslib.git+ +
     +LIBFOO_SITE=/opt/software/libfoo.tar.gz+ +
     +LIBFOO_SITE=$(TOPDIR)/../src/libfoo/+
 

docs/manual/adding-packages-tips.txt

@@ -41,11 +41,12 @@ How to add a package from github
 
 Packages on github often don't have a download area with release tarballs.
 However, it is possible to download tarballs directly from the repository
-on github.
+on github. As github is known to have changed download mechanisms in the
+past, the 'github' helper function should be used as shown below.
 
 ------------------------
 FOO_VERSION = v1.0 # tag or full commit ID
-FOO_SITE = http://github.com/<user>/<package>/tarball/$(FOO_VERSION)
+FOO_SITE = $(call github,<user>,<package>,$(FOO_VERSION))
 ------------------------
 
 .Notes