Add rc.resume(8) alias for rc(8) to fix the manpage cross references
This issue was noticed when running make manlint as part of MFCing r342597 to
^/stable/11:
$ make -C share/man/man8 rc.8lint mandoc -Tascii -Tlint rc.8 mandoc: rc.8:548:6: STYLE: referenced manual not found: Xr rc.resume 8 $
This is a followup commit to r339818.