Update build instructions

README.md

@@ -1,6 +1,21 @@
 # Notes server
 
-## Build and run
+## Set up mkdocs and build HTML
+
+````bash
+# Set up a Python virtualenv for mkdocs.
+sudo apt install virtualenv
+virtualenv .venv
+. .venv/bin/activate
+
+# Install mkdocs.
+pip install mkdocs
+
+# Build the HTML.
+mkdocs build
+```
+
+## Build and run server
 
 ```bash
 # Set access credentials.
@@ -11,7 +26,7 @@ docker build --no-cache -t notes-server .
 
 # Run the image, listening on port 42069.
 docker run --mount type=bind,src=./site,dst=/usr/share/nginx/html -p 42069:80 -t notes-server
-```
+````
 
 ## Auth credentials setup