README change: corrected the "Run the Arquillian Tests" section

* emphasized the importance of Arquillian
* corrected and minimised the usage of the word "container" throughout the section, as it can be ambiguous
* described configuration options of arq remote container and emphasize that it can actually be used to run tests on different machines
* corrected usage of "test/resources/arquillian.xml" to "src/test/resources/arquillian.xml"
* the "managed container" section incorrectly contained mentions of a remote container
* mentioned the possibility to use JBOSS_HOME env var
* I found the managed container section too verbose, I think there's no need for two code snippets, one is plenty