The `bud` sub-command has been a hidden alias to `build` for quite a
while.  Fix the documentation accordingly.

Signed-off-by: Chris Evich <cevich@redhat.com>

All/most markdown renderers will mask any naked `<` and `>` characters
that appear in the plain text.  This was making the documented syntax
of the `ARG` command unintelligible.  Fix this.

Signed-off-by: Chris Evich <cevich@redhat.com>

Available for quite some time, but often useful and undocumented.
Fix that and a minor whitespace problem.

Signed-off-by: Chris Evich <cevich@redhat.com>