Fix markdown formatting

Author: mjambon

src/README.md

@@ -4,5 +4,7 @@ OCaml sources for dune-deps
 `lib`: source files containing the core functionality of the
        application, used by the main executable and the unit test
        suite.
+
 `bin`: command-line interface, produces `dune-deps` executable.
+
 `test`: unit tests for `lib`, producing one executable.