New vignette + bug fixes

[pepaaran]

This Pull Request includes:

• The functions collect_drivers_sofun and prepare_setup_sofun were deleted from rsofun and added to ingestr.
• Typo in README corrected (installation of devtools)
• Bug fix: Paths to individual files were wrong for ingesting WATCH-WFDEI data (wrote // rather than /)
• Vignette "Ingest P-model drivers from coordinates": Whole workflow to get rsofun forcing for a given location (not necessarily flux sites), format data into p_model_drivers format, aggregate data into an "average year of forcing" and finally run the P-model.

[pepaaran]

@stineb I added the final version for the vignette (get forcing for non-flux sites) to the pull request. The package installation works for me but I couldn't run the checks locally because some need to be run in Euler. In any case, the majority of checks are passed so you probably can safely merge the PR. Thanks!

[stineb]

Thanks @pepaaran !