Update DEVELOPERS.md

DEVELOPERS.md

@@ -355,3 +355,17 @@ Add exports in `index.ts` for the new classes:
 export * from "./addition";
 export * from "./addition_params";
 ```
+
+## How to set up a new hydraulic structure equation
+
+@TODO
+
+### structure type
+
+### structure class
+
+### admissible laws
+
+### structures factory
+
+### session