Update windows/README

The build instructions have changed somewhat, as have the requirements
for a build environment.
The default behavior for KRB5_CONFIG and KRB5CCNAME has also changed.
Attempt to remove mention of overly specific Windows versions that
are now quite old when the behavior persists in newer versions of Windows.
Document the usage of DNS by default and the reduced need for a large
krb5.ini file.
Talk a little more about the LSA cache.

The kerbsrc.win target is no longer supported.

(cherry picked from commit d77308a1eaf9c996e10fbc2f82e79c4df3fc1078)

https://github.com/krb5/krb5/commit/404d87abcf564424eb18ba336cf08593b237e485
Author: Ben Kaduk <kaduk@mit.edu>
Committer: Tom Yu <tlyu@mit.edu>
Commit: 404d87abcf564424eb18ba336cf08593b237e485
Branch: krb5-1.10
 src/windows/README |  191 +++++++++++++++++++++++++---------------------------
 1 files changed, 92 insertions(+), 99 deletions(-)