ENV variables are not appropriately set

[scottdangelo]

According to the README 4. Install dependencies to build the mobile application after installing the dependencies:

Once you have completed all of the required installs and setup, you should have the following environment variables set appropriately for your platform:

JAVA_HOME
ANDROID_HOME
PATH

However, these are not set. It appears that they must be set manually, and the instructions point to the Troubleshooting link.
But if these must be set, they are not "Troubleshooting", and the instructions should be in the steps, as they are absolutely required.
Also, the Troubleshooting instructions do not mention setting JAVA_HOME. This should also be documented.

[scottdangelo]

figuring out JAVA_HOME took some searching, so it'd be good to give explicit instructions.
jdk can be found by:

/usr/libexec/java_home

and the export can be done with:

export JAVA_HOME=`/usr/libexec/java_home`

[RiyaMRoy04]

@scottdangelo Good inputs! Would you like to send a PR with these edits?