mongrel2: Add comments to avoid use of github call

As the comment says, we don't want to uses the github helper, as we
would end up with a generated tarball, which is not the same one as the
one linked with the releases.

Signed-off-by: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/mongrel2/mongrel2.mk

@@ -5,6 +5,8 @@
 ################################################################################
 
 MONGREL2_VERSION = v1.9.1
+# Do not use the github helper here, the generated tarball is *NOT* the same
+# as the one uploaded by upstream for the release.
 MONGREL2_SITE = https://github.com/zedshaw/mongrel2/releases/download/$(MONGREL2_VERSION)
 MONGREL2_LICENSE = BSD-3c
 MONGREL2_LICENSE_FILES = LICENSE