Add README to docs folder

docs/README.md

@@ -0,0 +1,8 @@
+# PySR Documentation
+
+## Building locally
+
+1. In the base directory, run `pip install -r docs/requirements.txt`.
+2. Install PySR in editable mode: `pip install -e .`.
+3. Build doc source with `cd docs && ./gen_docs.sh && cd ..`.
+4. Create and serve docs with mkdocs: `mkdocs serve -w pysr`.