Codecov how-to in CI section

[ewallace]

• Explain how to use Codecov in coverage / continuous integration section.
• Added brief "What is CI" section

As discussed with @maelle and @mpadge in
https://discuss.ropensci.org/t/staff-admin-team-codecov/2982/3
ropensci/tidyqpcr#191

[mpadge]

Thank you very much @ewallace for this clear improvement in both structure and wording. Our Dev Guide is intended to be a community effort, and we particularly appreciate this kind of direct engagement with its ongoing development. I've made a couple of minor suggestions, and only the one not-really-minor request for change. Happy to iterate and discuss further as you see fit.

[maelle]

Thank you! Two other comments: please add yourself to

dev_guide/index.Rmd

Line 72 in 55eba7e

_We are thankful for all authors, reviewers and guest editors for helping us improve the system and this guide over the years. Thanks also to the following persons who made contributions to this guide and its previous incarnations: [Katrin Leinweber](https://github.com/katrinleinweber), [John Baumgartner](https://github.com/johnbaums), [François Michonneau](https://github.com/fmichonneau), [Christophe Dervieux](https://github.com/cderv), [Lorenzo Busetto](https://github.com/lbusett), [Ben Marwick](https://github.com/benmarwick), [Nicholas Horton](https://github.com/nicholasjhorton), [Chris Kennedy](https://github.com/ck37), [Mark Padgham](https://github.com/mpadge), [Jeroen Ooms](https://github.com/jeroen), [Sean Hughes](https://github.com/seaaan), [Jan Gorecki](https://github.com/jangorecki), [Joseph Stachelek](https://github.com/jsta), [Dean Attali](https://github.com/daattali), [Julia Gustavsen](https://github.com/jooolia), [Nicholas Tierney](https://github.com/njtierney), [Rich FitzJohn](https://github.com/richfitz), [Tiffany Timbers](https://github.com/ttimbers), [Hilmar Lapp](https://github.com/hlapp), [Miles McBain](https://github.com/milesmcbain), [Bryce Mecum](https://github.com/amoeba), [Jonathan Carroll](https://github.com/jonocarroll/), [Carl Boettiger](https://github.com/cboettig/), [Florian Privé](https://github.com/privefl), [Stefanie Butland](https://github.com/stefaniebutland), [Daniel Possenriede](https://github.com/dpprdan/), [Hadley Wickham](https://github.com/hadley/), [Mauro Lepore](https://github.com/maurolepore/), [Matthew Fidler](https://github.com/mattfidler), [Luke McGuinness](https://github.com/mcguinlu), [Aaron Wolen](https://github.com/aaronwolen), [Indrajeet Patil](https://github.com/IndrajeetPatil), [Kevin Wright](https://github.com/kwstat), [Will Landau](https://github.com/wlandau), [Hugo Gruson](https://github.com/Bisaloo),

and a news item to

dev_guide/appendix.Rmd

Line 6 in 55eba7e

[ewallace]

Thanks @mpadge and @maelle - I've made the changes requested, HTH.

[maelle]

thanks so much!