Add initgame.txt

* Add the file for erl -args_file ./initgame.txt
Add e.erl

* NOTE WELL: This is solely for REPL shortcut of
  erltrek_game:enterprise_command/1.
  Keep commands short, and don't you ever treat this one-letter-name
  module as a *generic* one!
  The module name is subject to change.
Update README.md

* Add explanations on initgame.txt and e.erl