diff --git a/.gitignore b/.gitignore
index 090a1f0..0fb8ed1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 .idea
 .DS_Store
+_build/
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
new file mode 100644
index 0000000..c403965
--- /dev/null
+++ b/CONTRIBUTING.md
@@ -0,0 +1,22 @@
+# Developer guide
+
+## Building the docs locally
+
+Install Python 3.11.
+
+Then run:
+
+```sh
+READTHEDOCS_VIRTUALENV_PATH=~/.virtualenvs/ena-read-docs
+READTHEDOCS_OUTPUT=./_build
+python -mvirtualenv $READTHEDOCS_VIRTUALENV_PATH
+source "$READTHEDOCS_VIRTUALENV_PATH/bin/activate"
+python -m pip install --upgrade pip setuptools
+python -m pip install --upgrade sphinx readthedocs-sphinx-ext
+python -m pip install --exists-action=w --no-cache-dir -r requirements.txt
+python -m sphinx -T -E -b html -d $READTHEDOCS_OUTPUT/doctrees -D language=en . $READTHEDOCS_OUTPUT/html
+```
+
+These are the same commands that are run on ReadTheDocs.
+
+You can adjust the variables `READTHEDOCS_VIRTUALENV_PATH` and `READTHEDOCS_OUTPUT` to your liking.