replace links to previous version of R-ecology-lesson

[tobyhodges]

Partly addresses #1035

This updates some of the links to the previous version of R-ecology-lesson. There are a few left that I am unsure of how to handle.

• in readings/R-intro.md, there is a link to [Introduction to R](http://www.datacarpentry.org/R-ecology-lesson/01-intro-to-r.html). The problem here is that the redesigned lesson takes a "ggplot2-first" approach, and I am not sure if that episode introduces the concepts you want at this stage of the course.
• in readings/R-databases.md, there is a link to [Data Management with SQL for Ecologists](https://datacarpentry.org/sql-ecology-lesson/). The redesigned lesson does not include content on dbplyr, so I cannot provide a ready replacement for this link. Sorry!

Any thoughts on how these two cases should be handled, @ethanwhite?

[github-actions]

Pa11y testing results

> pa11y-ci:sitemap
> pa11y-ci --sitemap http://localhost:4000/semester-biology/sitemap.xml --sitemap-exclude "/*.pdf|Knitr-BBS-R.html|paper.*"

The sitemap "http://localhost:4000/semester-biology/sitemap.xml" could not be loaded

[ethanwhite]

Thanks for the PR @tobyhodges and for your patience.

For the Intro reading let's replace it with these two pages:

• https://intro2r.com/getting-started.html
• https://intro2r.com/objects-in-r.html

For the databases the existing link is fine since it's to the SQL lesson and the second link (non-Data Carpentry; but also broken) is the one related to dbplyr.

So just add those two links for the R-Intro stuff and I'll get this merged. Thanks!

[tobyhodges]

Done! Thanks @ethanwhite

[github-actions]

Pa11y testing results

> pa11y-ci:sitemap
> pa11y-ci --sitemap http://localhost:4000/semester-biology/sitemap.xml --sitemap-exclude "/*.pdf|Knitr-BBS-R.html|paper.*"

The sitemap "http://localhost:4000/semester-biology/sitemap.xml" could not be loaded

[ethanwhite]

Thanks @tobyhodges!