Fix Makefile dist target.
This may not be the best solution if you'd prefer to have the README without extension in the dist tarball; then an additional target should likely be created to copy README.adoc to README (as done in !39 (merged)).
This may not be the best solution if you'd prefer to have the README without extension in the dist tarball; then an additional target should likely be created to copy README.adoc to README (as done in !39 (merged)).