Update links to EE getting started guide.

[samccann]

The execution environment getting started guide as move to https://ansible.readthedocs.io/en/latest/getting_started_ee/index.html

Update the url introduced in #1301 to point to the new location.

[SirSEA]

Having challenge locating the url introduced in #1301

[samccann]

Hi @SirSEA and thanks for taking a look at this! The url that needs to change is at https://github.com/ansible/ansible-runner/blob/devel/docs/execution_environments.rst?plain=1#L8

And replace it with https://ansible.readthedocs.io/en/latest/getting_started_ee/index.html