docs: add setup guide in the readme.md file for building documentation

README.md

@@ -9,6 +9,24 @@ Main sections:
 - [Projects](https://numfocus.github.io/infrastructure/projects/index.html): Information regarding NumFOCUS projects that use shared infrastructure
 - [Vendors](https://numfocus.github.io/infrastructure/vendors/index.html): Information about NumFOCUS infrastructure providers (e.g., hosting companies)
 
+## Building locally
+
+You can create your own Python virtual environment and do the following:
+
+```bash
+pip install -r requirements.txt
+cd docs
+make html
+sphinx-build -b html . _build/html
+```
+
+Or you can use tox:
+
+```bash
+pip install tox
+tox -e build_docs
+```
+
 ## Contact
 
 [To contact the committee, you can use the email address: infrastructure@numfocus.org](infrastructure@numfocus.org)