Add some trouble shooting docs

docs/Makefile

@@ -1,7 +1,7 @@
 .POSIX:
 
 todo:
-	printf "# TODO\n\n" > TODO.md
+	printf "# TODO\n\n" > todo.md
 	git grep --line-number TODO .. ':!.' \
 		| awk --field-separator ':| TODO ' '{ printf "- [%s](%s#L%s)\n", $$4, $$1, $$2 }' \
-		>> TODO.md
+		>> todo.md

docs/troubleshooting.md

@@ -0,0 +1,19 @@
+# Trouble shooting
+
+## Bare metal
+
+### Nodes not booting from the network
+
+- Plug a monitor and a keyboard to one of the bare metal node if possible to make the debugging process easier
+- Check if the controller (PXE server) is on the same subnet with bare metal nodes (sometimes Wifi will not work or conflict with wired Ethernet, try to turn it off)
+- Check if bare metal nodes are configured to boot from the network
+- Check if Wake-on-LAN is enabled
+- Check if the operating system ISO file is mounted
+- Check the controller firewall config
+- Check PXE server Docker logs
+
+## Cloud infrastructure
+
+### RKE cannot connect to the LXC nodes
+
+- Check if you can SSH to the node(s) using the configured SSH key