docs: require cfg.bindings entry for account->agent routing

agent=account only routes correctly when openclaw cfg.bindings has a
{agentId, match:{channel:fabric, accountId}} entry; else falls back to
the default agent. Verified: with the binding, account echo -> agent
echo, reply posted back as the agent.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -25,9 +25,23 @@ the identity file.
 ## Config
 
 - `channels.fabric.centerApiBase` — e.g. `http://localhost:7001/api`
+- `channels.fabric.accounts.<agentId>` = `{ fabricApiKey, enabled }`
+  (agent = account; the account id is the openclaw agentId)
 - plugin `identityFilePath` — default `~/.openclaw/fabric-identity.json`
   (`{ entries: [{ agentId, fabricApiKey }] }`)
 
+### Required: route binding (account → agent)
+
+openclaw routes a channel turn to an agent via `cfg.bindings`. Without a
+Fabric binding it falls back to the default agent. Add one per account:
+
+```json
+{ "agentId": "<agent>", "match": { "channel": "fabric", "accountId": "<account>" } }
+```
+
+e.g. `openclaw config set bindings '[…, {"agentId":"echo","match":{"channel":"fabric","accountId":"echo"}}]' --json`,
+then `openclaw gateway restart`.
+
 ## Tools
 
 - `fabric-register` — bind this agent's Fabric API key