Fix missing markdown include in manifest (#1274)

Co-authored-by: Baptiste Jonglez <git@bitsofnetworks.org>
(cherry picked from commit 2ce1ea4)

Author: zorun

MANIFEST.in

@@ -1,3 +1,3 @@
-include *.rst
-recursive-include ihatemoney *.rst *.py *.yaml *.po *.mo *.html *.css *.js *.eot *.svg *.woff *.txt *.png *.webp *.ini *.cfg *.j2 *.jpg *.gif *.ico *.xml
-include LICENSE CONTRIBUTORS CHANGELOG.rst
+include *.md
+recursive-include ihatemoney *.py *.yaml *.po *.mo *.html *.css *.js *.eot *.svg *.woff *.txt *.png *.webp *.ini *.cfg *.j2 *.jpg *.gif *.ico *.xml
+include LICENSE CONTRIBUTORS