Update of documentation for #4223

[jmorris-uk]

Description

Minor change to documentation pages to reflect:

• there is no longer a "default" process IN.DAT and
• if process is run with no input file given it no longer will look for a file called IN.DAT, it will run process --help.

Checklist

I confirm that I have completed the following checks:

• My changes follow the PROCESS style guide
• I have justified any large differences in the regression tests caused by this pull request in the comments.
• I have added new tests where appropriate for the changes I have made.
• If I have had to change any existing unit or integration tests, I have justified this change in the pull request comments.
• If I have made documentation changes, I have checked they render correctly.
• I have added documentation for my change, if appropriate.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 50.23%. Comparing base (60443bd) to head (378ed99).
⚠️ Report is 19 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4241      +/-   ##
==========================================
- Coverage   51.40%   50.23%   -1.18%     
==========================================
  Files         151      151              
  Lines       30055    29365     -690     
==========================================
- Hits        15451    14752     -699     
- Misses      14604    14613       +9     

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[clmould]

A bit of rearranging please (see comments)

Also, there is a reference to a default IN.DAT in input-guide.md - could this be removed as well please?

[clmould]

While you're here, could you update this list of output files please as this is no longer correct, eg here are the outputs I got from running examples/data/large_tokamak_IN.DAT with --full-output:

[jmorris-uk]

Done

[clmould]

These sentences aren't needed any more

[jmorris-uk]

Not sure why these aren't needed? It explains they need to end in IN.DAT and if you run with no input file it prints the help message.

[clmould]

Sorry worded this badly as I gave no explanation! The bit about ending in IN.DAT is already below (on line 21), and then the bit about process giving the help menu can be moved down to join the bit already on line 70, so all this information will stay here, just rearranged a tad. I think referencing 'running without an input file' isn't as clear as instead saying running process will give the help message

[clmould]

This can be moved further down (see later comment), so this section can begin with 'The user can provide a named input file...'