spelling corrections in readme files

Fix spelling errors in readme files.

Change-Id: I62348372d5e226f2b2a3a7732b4a5f8c7331b2ff
Reviewed-on: http://gerrit.openafs.org/8876
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Ken Dreyer <ktdreyer@ktdreyer.com>