Updated readme to counter issues #197

[jk1ng]

Readme.md now tells users to ensure that their PATH and JAVA_HOME (or JDK_HOME) environment variables must be set properly in order to ensure the successful usage of PyJNIus. This should help counter issues #197 -- not the most automated fix, but still.

Apologies for the triple commit, apparently I don't know how to use markdown properly :)

[jk1ng]

As an addendum, this doesn't solve #199 -- danielepantaleone's PR #200 does that.

[danielepantaleone]

You should squash all those commits together to keep a clean git history.
Also I think the problem should be addressed at a certain point. I had the very same problem in the application I'm using PyJNIus in and I have added some code to automatically lookup the JVM path on different operating systems in case the JAVA_HOME and Path variables are not setup correctly. Something similar to what JPype is doing....not a very clean approach imho, but it would be better than nothing.

[akshayaurora]

@jk1ng thanks