Add an In Memoriam file to complement CREDITS

While I was going through the CREDITS file the other day, I couldn't
help but notice that 2 people in there had passed away.  So I thought
it would be nice to commemorate them more extensively in a separate
file, to be able to credit their work better, and keep their memories
alive.

Please note that this by no means is intended to be the final version
of this file.  If you feel like you have something to add to it, or
feel that corrections should be made, then please open up an issue,
or create a Pull Request for it.  Thank you!

IN-MEMORIAM.md

@@ -0,0 +1,35 @@
+The people mentioned here have been contributors to the various stages of
+the development of the Raku Programming Language, but unfortunately have
+departed this existence.  We thank them for their contributions and hope
+to keep their memory alive here, as well as other places.
+
+Jonathan Scott Duff (perlpilot)
+-------------------------------
+In the early days of the Rakudo implementation, Jonathan Scott Duff
+implemented many of the NQP and Raku features that we take for granted
+now.  In later years, he kept a very observant eye on developments in
+the Rakudo and NQP code.
+
+From the obituary at: https://www.legacy.com/obituaries/caller/obituary.aspx?n=jonathan-scott-duff&pid=191217621
+
+> Born in Baton Rouge, La. and raised in Corpus Christi, TX, he passed away at the age of 47 in his home in Fort Worth, TX on Friday, Dec. 28, 2018 after battling cancer.
+> He was a beloved husband, father, and friend. He is survived by his devoted wife, Cynthia; four children, Jazmine, Christian, Camryn, and Joseph, all of Fort Worth, Tx; his loving mother, Linda T Duff of LaPlace, La.; brothers, Brian Duff of Corpus Christi, TX, and Allen Duff of LaPlace, La; and many nieces and nephews. He was preceded in death by his father, Grady W. Duff, Jr 'Dub'.
+
+Jeff Goff (DrForr)
+------------------
+Ever since Jeff Goff got involved in the Perl community, he could be
+found helping people. He was very active at events and conferences:
+giving presentations, volunteering, and gaming with other attendees.
+
+He also supported development as a release manager for the Parrot project.
+Many have benefitted from his online presence, always ready to
+help and answer questions.
+
+He died in March 2020 in a snorkelling accident.
+
+
+Final words
+-----------
+If you have any suggestions for additions, changes or other comments,
+please create an issue for it, or even better, a Pull Request, so that
+we can give these people all the credit they deserve.