Need actual examples of TDD PRs for readme

[hadley]

Start on a list using https://github.com/issues?page=2&q=is%3Aissue+is%3Aclosed+archived%3Afalse+label%3A%22tidy-dev-day+%3Anerd_face%3A%22

• https://github.com/tidyverse/tidyr/issues/865 / https://github.com/tidyverse/tidyr/pull/866
• https://github.com/tidyverse/readr/issues/1057 / https://github.com/tidyverse/readr/pull/1070
• https://github.com/tidyverse/purrr/issues/671 / https://github.com/tidyverse/purrr/pull/689
• https://github.com/tidyverse/ggplot2/issues/3753 / https://github.com/tidyverse/ggplot2/pull/3771

Bigger issues

• https://github.com/tidyverse/dplyr/issues/4755 / https://github.com/tidyverse/dplyr/pull/4825

Non-documentation:

• https://github.com/tidyverse/forcats/issues/233 / https://github.com/tidyverse/forcats/pull/240
• https://github.com/r-lib/cli/pull/132 / https://github.com/r-lib/cli/issues/128

[hadley]

A good example of a very detailed issue is https://github.com/r-lib/pkgdown/issues/2727