Document how to run the performance benchmark standalone and link this from performance runs

Create an article on our wiki (or maybe better done by updating the https://github.com/jbosstm/performance/blob/master/README.md) and then link it from the performance output.

It doesn't need to say how to run against the PR I would say, that can be left to the reader.

Nothing too heavy, just the general flags and how to run it.
git clone narayana master
git clone performance master
(cd narayana && ./build.sh -DskipTests)
(cd performance && ./build.sh -DskipTests)
cd performance
export JMH_ARGS=...
./build.sh...