Add a THANKS file.

* THANKS: New file.
* Makefile.am: Distribute it.

Makefile.am

@@ -22,6 +22,7 @@ include $(top_srcdir)/build-aux/guile.am
 EXTRA_DIST +=                                   \
   .dir-locals.el                                \
   COPYING.CC0                                   \
+  THANKS                                        \
   bootstrap                                     \
   build-aux/git-version-gen                     \
   build-aux/gitlab-ci.yml                       \

THANKS

@@ -0,0 +1,21 @@
+Acknowledgements
+****************
+
+A warm thanks to:
+
+Ineiev for reviewing the copyright and license notices.
+
+Donald R. Robertson, III for help with the CC0 dedication.
+
+Emily Hopkins for proofreading the manual and providing helpful
+suggestions.
+
+Copying this file
+=================
+
+Copyright © 2019 Timothy Sample <samplet@ngyro.com>
+
+Copying and distribution of this file, with or without modification,
+are permitted in any medium without royalty provided the copyright
+notice and this notice are preserved.  This file is offered as-is,
+without any warranty.