selinux.rst: point to the correct file

selinux.rst: point to the correct file

The selinux documentation mentions to check the selinux/openvswitch.te file
for any permissions that might need to be added.  However, the commit
7bc1aae71e89 ("rhel: make the selinux policy intermediate") moved this
file to be generated from intermediate file selinux/openvswitch.te.in
instead.

Correct the documentation, so that users won't be trying to edit a generated
file.

Also, add a gitignore for the autogenerated file.

Fixes: 7bc1aae71e89 ("rhel: make the selinux policy intermediate")
Reported-by: Ansis Atteka <aatteka@ovn.org>
Signed-off-by: Aaron Conole <aconole@redhat.com>
Acked-by: Ansis Atteka <aatteka@ovn.org>