add crates/README.md

crates/README.md

@@ -0,0 +1,30 @@
+## Dependency diagram of the project
+
+```mermaid
+graph TD;
+    lavina-->mgmt-api;
+    lavina-->projection-irc;
+    lavina-->projection-xmpp;
+    lavina-->lavina-core;
+
+    projection-irc-->proto-irc;
+    projection-irc-->lavina-core;
+    
+    projection-xmpp-->proto-xmpp;
+    projection-xmpp-->lavina-core;
+
+    sim-irc-->proto-irc;
+    sim-irc-->mgmt-api;
+
+    sim-xmpp-->proto-xmpp;
+    sim-xmpp-->mgmt-api;
+
+    workspace-->lavina;
+    workspace-->sim-irc;
+    workspace-->sim-xmpp;
+```
+
+A few rules:
+- Only projections should be direct deps of `lavina`, there is no need to depend on `proto-*` crates.
+- On the other hand, projections should not be dependencies of `sim-*` crates.
+- `lavina-core` does not depend on protocol-specific crates.