README installation instructions

[slmcevoy]

I ran into a couple of issues following the installation instructions:

docker run -itd -p 8080:80 -p 5432:5432 --name tripal3 -v .:/modules/mycustom statonlab/tripal3
docker: Error response from daemon: create .: volume name is too short, names should be at least two alphanumeric characters.

I had to use a path for the volume, not a '.'

Mac for OS /var symlinked to /private/var so I had to modify the Dockerfile WORK_DIR to /private/var/www/html

After that this command worked:
docker run -itd -p 8080:80 -p 5432:5432 --name tripal3 -v /private/var/www/html:/modules/mycustom statonlab/tripal3

[bradfordcondon]

thank you for the feedback! we'll get to fixing this after the hackathon probably.

👍