Add pre-commit documentation to README [#9]

README.md

@@ -5,3 +5,16 @@ Phylogenies of human seasonal coronaviruses.
 Built starting from the [Nextstrain pathogen repository template][].
 
 [Nextstrain pathogen repository template]: https://github.com/nextstrain/pathogen-repo-guide/
+
+## Working on this repo
+
+This repo is configured to use [pre-commit](https://pre-commit.com).
+If you will be writing new code or otherwise working within this repo,
+please do the following to get started:
+
+1. install `pre-commit` by running either `python -m pip install
+   pre-commit` or `brew install pre-commit`, depending on your
+   preferred package management solution
+2. install the local git hooks by running `pre-commit install` from
+   the root of the repo
+3. get to coding!