Flesh out the configuration documentation

Flesh out the configuration documentation

Remove obsolete configure options and document all remaining options
other than some provided by Autoconf and some that are currently not
very interesting.

Document that, on modern Linux systems, configure can find the kernel
build system and headers by itself and doesn't need the flag.

Include some more information in README about changing the default
installation paths, and mention that the da* versions of the file server
and volserver also aren't stripped.

Remove the generic GNU installation instructions, which aren't useful
for OpenAFS.

Change-Id: I56d0003ff0173749e9a5e04f1d0ed4d004787dfd
Reviewed-on: http://gerrit.openafs.org/2438
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>