FillValue for PARAM

[vturpin]

Following recommendation of #102 to clarify how to manage fix values

Proponents:
Moderator: @OceanGlidersCommunity/format-mantainers

Type of PR

• Typo without possible change of interpretation of the related text.
• Fix of some error, inconsistency, unforeseen limitation.
• Style that only affects visually the compiled document
• Addition that does not require change in the current structure.
• Enhancement that require changes to improve the format.

Related Issues

Dates when it got review approvals

The suggestion made by @castelao has been made a month ago.
So I push a PR to close the issue

Release checklist

• Approved by at least two members of the committee?
• There were modifications after the review approvals? If so, please
  ask reviewers to update their review.
• Proponents and moderador should explicitly agree that it is ready to
  to merge.
• The moderador is the one in charge to actually merge or close this PR
  according to the final decision.

For maintainers

• Update the moderator with a volunteer from the committee. It would be
  best to have one single moderator to guide and help this PR to move
  forward. It is OK to update the moderador pass it to another one.
• Confirm that the associated branch was deleted after the merging.
• Wrap-up and close the related issues.

Comments

[justinbuck]

Discussed at OG 1.0 meeting 24th April 2023, is inconstant with geophysical variables section.
Updated recommendation based on feedback needed.

[justinbuck]

Approved by consensus at OG 1.0 meeting 24th April 2023