Read ES_HOME, APP_NAME and APP_LONG_NAME from JVM config file

This patch modifies the init.d service script to read existing values for elasticsearch home path and app name (service name) from elasticsearch.conf

Like this,  the wrapper is location independent on Linux. It is no longer required to be placed in bin of elasticsearch!
I can't tell the same about Windows (I don't know), that's why I moved that requirement in the Readme to the Windows section.

Thank you!