Improve docstrings

[ArnoStrouwen]

Such that makedocs warnonly = [:missing_docs] can be removed.

[Spinachboul]

@ArnoStrouwen
Can you also provide the reference for this issue!

[ArnoStrouwen]

Solve these warnings here:
https://github.com/SciML/GlobalSensitivity.jl/blob/master/docs/make.jl#L15
Likely, putting the checkdocs keyword to :exports will get you 90-100% of the way there:
https://documenter.juliadocs.org/stable/lib/public/#Documenter.makedocs,
since most of the warnings are false positives (we only want to document the external API, not all internals).

[Spinachboul]

@ArnoStrouwen
So basically, in this code : https://github.com/SciML/GlobalSensitivity.jl/blob/master/docs/make.jl#L15
we have to replace warnonly = [:missing_docs] by checkdocs = :exports.
This change also has to be done in the docs which would reduce the false positive warnings

Please tell me if I am going along the correct lines

[ArnoStrouwen]

By removing the warnonly keyword, Documenter will error when building the documentation if there is anything in the package which does not have a docstring included in the Documentation.
(things like: https://docs.sciml.ai/GlobalSensitivity/stable/methods/morris/)
By setting the checkdocs keyword to exports, it will only error if the missing docstrings are attached to something that is actually exported by the package, which is the behavior we want.

It might be that everything is already included, in that case nothing extra needs to be done.
It might be that a docstring is missing, in which case it needs to be either added to the appropriate place in the methods section of the documentation, or alternatively, it might be something that did not need to be exported.