MANIFEST.in: include .dot files under docs

MANIFEST.in

@@ -1,7 +1,7 @@
 include versioneer.py
 include src/wormhole/_version.py
 include LICENSE README.md NEWS.md
-recursive-include docs *.md *.rst
+recursive-include docs *.md *.rst *.dot
 include docs/wormhole.1 docs/wormhole-server.8
 include .coveragerc tox.ini snapcraft.yaml
 include misc/windows-build.cmd