Attach to existing JVM documentation

[marlow-fawn]

I couldn't find any documentation for using an existing JVM - is it possible to add an example somewhere in the docs?

          It is possible with some modifications.    In android we use an existing JVM to run JPype.   It is just a matter to some patching the startJVM and the C++ to match the android path to use an existing JVM rather than spawn a fresh copy.

Originally posted by @Thrameos in #1084 (comment)

[Thrameos]

I completed that as a demo for KIVY folks. I ran all of the JPype test bench with only one failure (some issue with JNI acting differently resulting in a crash but is was a rare edge case). Unfortunately the KIVY folks never picked up the ball to test it beyond my runs in the emulator. The ANDRIOD #if/#endif shows the changes that were needed. It has been about 3 years since I last ran it myself, but if someone with wants to get it running again and document it more it is doable.