Closes #1839 Add my_first_fcn for onboarding

[biocyberman]

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• Update to all relevant roxygen headers and examples, including keywords and families. Refer to the categorization of functions to tag appropriate keyword/family.
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• Build admiral site pkgdown::build_site() and check that all affected examples are displayed correctly and that all new functions occur on the "Reference" page.
  I actually got this error but it is irrelevant, and therefore I will ignore it for now:

Reading man/call_derivation.Rd
Error: 
! in callr subprocess.
Caused by error in `build_reference()`:
! Failed to parse Rd in call_derivation.Rd
Caused by error in `output_handler$source()`:
! argument "expr" is missing, with no default
ℹ See `$stdout` and `$stderr` for standard output and error.
Type .Last.error to see the more details.

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[github-actions]

Package	Line Rate	Health
admiral	96%	✔
Summary	96% (4953 / 5152)	✔

[manciniedoardo]

hello @biocyberman - looks good but i think you accidentally committed some renv files?

[manciniedoardo]

@biocyberman for the build_site error, what version of Roxygen do you have?

[manciniedoardo]

@biocyberman if you add adxx to inst/WORDLIST then the spellcheck won't flag it up as a misspelled word. then your dummy issue will be complete :)