simpler check and deps messages

rig/docs/notes/docs.md

@@ -0,0 +1,14 @@
+# ctrl/docs.sh
+
+## Serving without the cluster or python
+
+The docs are the instructions for building the cluster, so they must work before
+anything else exists. That rules out serving them from the cluster, and it rules
+out `python -m http.server` too — a minimal Debian has no python3. What it does
+have, by definition, is Docker: the single prerequisite rig already demands. So a
+throwaway nginx container serves a read-only bind mount.
+
+## Committed SVGs
+
+Rendered SVGs are committed alongside their `.dot` sources for the same reason:
+the pages have to read on a machine with no Graphviz installed.