Add Firefox user id 1001 to README common problems

[MikeMcC399]

This is a suggestion to add a note in README: Common problems to describe the issue about accessing the Firefox browser in a Docker image.

• Firefox README example in container github-action#735 described about running Firefox in a container and the README: Firefox section used to say:

"In order to run Firefox, you need to use non-root user (Firefox security restriction)."

"Note: the magical user id 1001 works because it matches permissions settings on the home folder, see issue #104"

In the meantime the Firefox example in https://github.com/cypress-io/github-action/blob/master/.github/workflows/example-firefox.yml does not use a Docker container anymore. Firefox was added to the GitHub runner images in March 2020, so it is no longer necessary to resort to using Firefox in a container as far as GitHub is concerned. Using Firefox from a container made the test set up and conditions for the GitHub Action unnecessarily complex.

So now there is no Cypress README document which mentions about using the magical user id 1001 to access Firefox in a container. For completeness, it should probably be described in this repository.

[alexjyong]

Per the request here, I'm going to open a PR to make this a reality. cypress-io/github-action#938 (comment)

[MikeMcC399]

• Thanks to @alexjyong this issue has been resolved by PR Update README.md to talk about non-root user for firefox per #938 in the github-action repo #900 and can now be closed!