Move the afs/DOC files to the top-leve doc/txt directory, since this has
become the home for developer oriented documentation.
Change-Id: I128d338c69534b4ee6043105a7cfd390b280afe3
Reviewed-on: https://gerrit.openafs.org/12662
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
