docs: flow modules convention

packages/orchestration/README.md

@@ -3,3 +3,18 @@
 Build feature-rich applications that can orchestrate assets and services across the interchain.
 
 Usage examples can be found under [src/examples](https://github.com/Agoric/agoric-sdk/tree/master/packages/orchestration/src/examples). They are exported for integration testing with other packages.
+
+## Orchestration flows
+
+Flows to orchestrate are regular Javascript functions but have some constraints to fulfill the requirements of resumability after termination of the enclosing vat. Some requirements for each orchestration flow:
+- must not close over any values that could change between invocations
+- must satisfy the `OrchestrationFlow` interface
+- must be hardened
+- must not use `E()` (eventual send)
+
+The call to `orchestrate` using a flow function in reincarnations of the vat must have the same `durableName` as before. To help enforce these constraints, we recommend:
+
+- keeping flows in a `.flows.js` module
+- importing them all with `import * as flows` to get a single object keyed by the export name
+- using `orchestrateAll` to treat each export name as the `durableName` of the flow
+- adopting `@agoric/eslint-config` that has rules to help detect problems