Add David M. Karr to credits

mdboom · mdboom · commit 99f4add1615d · 2018-08-07T10:56:32.000-04:00
diff --git a/source/credits.rst b/source/credits.rst
@@ -11,6 +11,7 @@ Michael Droettboom wishes to thank the following contributors:
 - Chris Carpenter
 - Christopher Mark Gore
 - David Branner
+- David Michael Karr
 - David Worth
 - E. M. Bray
 - Fenhl
