MFC r331696, r331697:

r331696:

Update the Release Engineering article URL to the modern version.

r331697:

Add an example for building SD card images for the RPI-B and RPI3.

Note, this commit manually fixes a merge conflict caused by r325096,
which does a seemingly recursive http -> https update, which this
commit was never marked for MFC.

Sponsored by: The FreeBSD Foundation