Appendix B suggests signals for a DMI with one DTM connected to one DM (#524)

* Appendix B: Added suggested signals for the DMI

* Added reference to the DMI implementation of the rocket-chip

Co-authored-by: Ernie Edgar <43148441+ernie-sifive@users.noreply.github.com>

* Converted bare hyper link into a latex href structure

* Added width to suggested DMI signals

* Added a reference from DMI to DMI signal suggestion

* Example read/write with the suggested DMI signals

* Moved suggested DMI signals into hardware implementations chapter

* Fixed spelling errors and improved wording for suggested DMI signals

Co-authored-by: Ernie Edgar <43148441+ernie-sifive@users.noreply.github.com>