Clarify that run_example files are not mean to be run by the user, they are for ci

[czoido]

We could add a comment to the files or something in the docs or any other soltion but I think it can be confusing for users finding them in the folder.
Related: #130
Related: conan-io/docs#3631

[czoido]

I think we could do a couple of things here:

• Change the name of the files to something less inviting to be run than run_example.py
• Check an environment variable that's set in the CI and output a message if it's not set (just a warning, do not fail)