Add switch to cli to allow choice between Chrome/Firefox

[jesse-osiecki]

• Add switch to cli to allow choice between Chrome/Firefox, keeping the -p headless flag as an option for both
• Default is Firefox as the previous changes defaulting to Chrome breaks previous functionality, Docker image doesn't have Chrome
• the install script is used by the Docker image, which doesn't have sudo. I propose reverting the addition of sudo within the script, and rather added verbiage to the README and script to run it with sudo

[jesse-osiecki]

@breenmachine@jstnkndy I propose adding a switch to the tool to allow a choice of browsers. I use Firefox headless so I was surprised when I pulled master and got Message: unknown error: cannot find Chrome binary

Currently I don't bake Chrome webdriver into the docker image, and while I am not opposed, I made this commit to keep the original functionality while extending the improvements that Justin made.

[breenmachine]

Hey Jesse, thanks so much for the PR. I agree it's nice to have both options. Merging it now.

[jesse-osiecki]

Thanks @breenmachine !