added docs directory, ros diagram

docs/architecture/node_interactions.md

@@ -0,0 +1,62 @@
+# ROS Node Interaction Document
+## Scope
+The purpose of this file is to descirbe the architecture of the RD25 stack from a ROS node level. This document should be updated whenever any ROS topics are added, removed or modified.
+
+## Viewing On VSCode
+Install `bierner.markdown-mermaid` from the extension marketplace to render the charts in VSCode markdown preview.
+
+## List of topics
+| Topic Name | Type                    | is custom message  |
+| ---------- | ----------------------- | ------------------ |
+| ego/state  | BuggyState              | yes |
+| other_buggy/state | BuggyState       | yes |
+| ego/trajectory | BuggyTrajectory     | yes |
+
+## ROS Nodes Graph
+Auton Loop [Sequence Diagram](https://en.wikipedia.org/wiki/Sequence_diagram#:~:text=A%20sequence%20diagram%20shows%2C%20as,order%20in%20which%20they%20occur.)
+
+```mermaid
+sequenceDiagram
+A->>B: "some/topic"
+```
+
+means A publishes a message of `some/topic` and B receives the message.
+
+```mermaid
+sequenceDiagram
+    participant I as Ego State Estimator Node
+    participant P as Planner Node
+    participant C as Controller Node
+    participant S as Firmware Comms Node
+
+    box Grey HBK 3DM-GQ7 INS
+        participant I
+    end
+
+    box Purple Auton Core
+        participant P
+        participant C
+    end
+
+    box Blue Communication with Sensors, Actuators and Other Buggy
+        participant S
+    end
+
+    loop 100hz
+        I->>P: "ego/state"
+        I->>C: "ego/state"
+    end
+
+    loop 10hz
+        S->>P: "other_buggy/state"
+    end
+
+    loop 10hz
+        P->>C: "ego/trajectory"
+    end
+
+    loop 100hz
+        C->>S: "ego/steering_cmd"
+    end
+```
+