Update release(7) to note OSRELEASE is only relevant when the
'install' target is invoked.

While here, bump the sample output version name, and explicitly
add the 'obj' target to avoid polluting the src checkout.

Submitted by: Trond Endrestol
PR: 243287 (related)
MFC after: 3 days
Sponsored by: Rubicon Communications, LLC (netgate.com)