docs: agent config was not under its correct section

Dockerfile

@@ -26,6 +26,7 @@ FROM node:22-alpine
 RUN apk add --no-cache ca-certificates
 RUN mkdir -p /var/lib/headplane
 RUN mkdir -p /usr/libexec/headplane
+RUN mkdir -p /var/lib/headplane/agent
 
 WORKDIR /app
 COPY --from=build /app/build /app/build

config.example.yaml

@@ -44,6 +44,7 @@ headscale:
 
 # Integration configurations for Headplane to interact with Headscale
 integration:
+  agent:
     # The Headplane agent allows retrieving information about nodes
     # This allows the UI to display version, OS, and connectivity data
     # You will see the Headplane agent in your Tailnet as a node when