Add example using {renv}

[brshallo]

{funspotr} requires that all packages are installed locally for the function to be identified as coming from that package. Add example of using {funspotr} with {renv} to ensure all needed packages are installed to local project environment.

[brshallo]

It may also be worth going through an example where you use renv::dependencies() in conjunction with spot_funs_custom()... may be worth opening a separate issue to look into making renv::dependencies() the internal engine of spot_pkgs().