Add note about why the images do not include Cypress binary pre-installed

[bahmutov]

Answer in #41 (comment)

[mtlynch]

This was pretty confusing for me as a new Cypress user. Generally the Docker image for $X contains $X ready to use. It would be sort of like running the mysql docker image and finding that it didn't actually contain mysql.

I understand from #41 that there are good reasons for doing it, but it would be helpful to make it more obvious to the user that cypress run won't just work out of the box.

[barnesicle]

Agreed. I thought there was something wrong with my Dockerfile, I was expecting cypress to be preinstalled, I thought that was the whole point

[fungiboletus]

@barnesicle Thanks for your work on the cypress/included images. They make a lot more sense in my humble opinion.

[bahmutov]

ok, closing this issue since we have cypress/included images