Refine the history of uname. It appeared in 4.4BSD. It was not in v7 unix. It

Refine the history of uname. It appeared in 4.4BSD. It was not in v7 unix. It
was one of the additions in PWB, and appeared in System III and later commercial
versions of Unix. The different args to uname weren't aded until System III. Add
a quick note to note the late entry into the BSD fork of Unix since PWB
otherwise implies a pre-fork date.