Bug 507292 - Create platform porting guide for 4.7 and update links in

Welcome page

See also https://git.eclipse.org/r/#/c/84801/

Change-Id: I6ba5e50bffb52abafd20f55c5f4bc77fbd8e2178
Signed-off-by: Sopot Cela <scela@redhat.com>