Improve doc for INSTALL_JOB

https://github.com/equinor/ert/blob/d8b17e4c7d1211cea135341501856028b77cccce/docs/reference/configuration/keywords.rst?plain=1#L421-L446

* Replace `Lomeland` with a more relevant example
* Don't claim it is easy
* Add a clickable link to the doc for the format of the "job" (fmstep) file

Open docs/reference/configuration/keywords.rst at lines 421-446 and read the INSTALL_JOB section. Replace the Lomeland example, remove the claim that it is easy, and add a clickable link to the documentation for the fmstep job-file format; the section is done when all three requested documentation changes are present.

Written by the indexing model from the issue text.