Reformat Markdown header syntax

README.md

-SableCC 3 - STUPS version
-===
+# SableCC 3 - STUPS version
 
 This work is based on SableCC 3.6 by Etienne Gagnon and others.
 
@@ -22,18 +21,16 @@ WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 Lesser General Public License for more details.
 
-License 
---- 
+## License
 
 This derived work is, like SableCC, covered by the GNU Lesser General Public License. You can view the copyright notice and the exact terms of the license in the files LICENSE, AUTHORS and COPYING-LESSER.
 
-Building
----
+## Building
 
 * Clone the repository.
 * Run the `assemble` target using Gradle (`./gradlew assemble` on Linux/macOS/etc., `gradlew.bat assemble` on Windows).
 * The binary is located in the build/libs subdirectory.
 
-Documentation
----
+## Documentation
+
 You can find complete and detailed documentation on the SableCC framework and syntax at the site http://sablecc.org/documentation.html