Add a rough system diagram from my notebook

The entities represented I believe are the bare minimum number of services
necessary to make things roughly work. The idea being that everything
effectively orients around the eventbus, and "extensibility" means tuning into
or publishing events rather than in-memory anything.

Fixes #20

Makefile

@@ -12,7 +12,6 @@ SUB_DIRS=grammar
 
 ################################################################################
 ## Phony targets
-
 # Cute hack thanks to:
 # https://marmelab.com/blog/2016/02/29/auto-documented-makefile.html
 help: ## Display this help text
@@ -39,7 +38,9 @@ prereqs: scripts/prereqs.sh ## Check that this system has the necessary tools to
 clean: ## Clean all temporary/working files
 	$(foreach dir, $(SUB_DIRS), $(MAKE) -C $(dir) $@)
 
-################################################################################
+diagram: system.png system.dot ## Generate the diagrams describing otto
+	dot -Tpng -o system.png system.dot
 
+################################################################################
 
 .PHONY: all build check clean depends lint swagger

system.dot

@@ -0,0 +1,29 @@
+digraph {
+    label="Otto system design";
+
+    node[shape="box", style="rounded"]
+
+    node[shape="box", style="square"]
+        orchestrator; frontend; datastore; objectstore; webhooks; agents;
+    node[shape="parallelogram", style=""]
+       eventbus;
+
+    webhooks -> eventbus[color="blue", label="write events"];
+    eventbus -> frontend[color="red", label="subscribe to live updates"];
+
+    orchestrator -> datastore[color="blue", label="create runs"];
+    orchestrator -> eventbus[color="purple", dir="both", label="read/write events"];
+    orchestrator -> agents[color="purple", dir="both", label="create and control agents"];
+
+    agents -> eventbus[color="blue", label="write events"];
+    agents -> datastore[color="blue", label="persist results"];
+    agents -> objectstore[color="blue", label="archive artifacts"];
+
+    datastore -> frontend[color="red", label="read runs"];
+    objectstore -> frontend[color="red", label="read artifacts"];
+    objectstore -> agents[color="red", label="fetch artifacts/stashes"];
+
+    //{rank=same; orchestrator agents eventbus}
+    //{rank=same; message input}
+}
+