Merge pull request #24 from wdduncan/patch-1

Update README.md

Author: balhoff

README.md

@@ -17,3 +17,9 @@ alternatively, the `owl` mode will output RDF, but as a valid OWL structure. The
 http://purl.obolibrary.org/obo/BFO_0000050
 http://purl.obolibrary.org/obo/BFO_0000051
 ```
+**Note:** Before running, you may need to increase the amount of memory available for Java. On UNIX style systems, this is done by setting the `JAVA_OPTS` environment variable. For example, to set the amount of memory to `16G`, you would use this command: `export JAVA_OPTS=-Xmx16G`.
+
+## Build
+Install `sbt` (Scala Build Tool) on your system. For Mac OS X, it is easily done using [Homebrew](http://brew.sh):  `brew install sbt`. `sbt` requires a working Java installation, but you do not need to otherwise install Scala.
+
+After `sbt` is installed, run `sbt stage` to create the executable. The executable is created in your `target/universal/stage/bin` directory.