Updated .gitignore to ignore test log dirs from project.
HOST_IP env var is used by entrypoint script to populate
the PCP config.
The entrypoint script does the following.
1. construct the PCP config file using the value of the env var
HOST_IP.
2. run elektron by providing all the basic command-line options.
Added build and run instructions in the README. These include
instructions to run elektron on bare-metal or using docker-compose.
