docs: improve store-related docs (#437)

* mention prefix and link to appropriate setting in known stores from ERR_ERL_DOUBLE_COUNT docs
* mention stores in readme example

---------

Co-authored-by: Vedant K <gamemaker0042@gmail.com>

docs/reference/error-codes.mdx

@@ -116,13 +116,19 @@ Set `validate: {positiveHits: false}` in the options to disable the check.
 This indicates that the hit count for a given IP or key was incremented more
 than once for a single request. It could happen if the same instance of
 express-rate-limit is called more than once, or if multiple instances are called
-that use the same Store.
-
-If only a single rate limit is desired, find and remove the extra rateLimit
-call(s).
-
-If multiple rate limits are desired, consider setting a custom `keyGenerator`
-for each to prevent double-counting.
+that use the same [Store](/reference/stores).
+
+- If only a single rate limit is desired, find and remove the extra rateLimit
+  call(s).
+
+- If multiple rate limits are desired, consider one of the following options:
+  - Set a custom `prefix` in the configuration for each store instance.
+    ([Redis](https://www.npmjs.com/package/rate-limit-redis#prefix),
+    [Memcached](https://www.npmjs.com/package/rate-limit-memcached#prefix),
+    [PostgreSQL](https://www.npmjs.com/package/@acpr/rate-limit-postgresql#constructor),
+    [Cluster](https://www.npmjs.com/package/@express-rate-limit/cluster-memory-store#prefix))
+  - Set a custom [`keyGenerator`](/reference/configuration#keygenerator) in the
+    configuration for each express-rate-limit instance.
 
 In rare circumstances this error can be a false positive. This would include
 situations where multiple rate limiters are configured to use the same key but

readme.md

@@ -38,7 +38,7 @@ const limiter = rateLimit({
 	limit: 100, // Limit each IP to 100 requests per `window` (here, per 15 minutes).
 	standardHeaders: 'draft-7', // draft-6: `RateLimit-*` headers; draft-7: combined `RateLimit` header
 	legacyHeaders: false, // Disable the `X-RateLimit-*` headers.
-	// store: ... , // Redis, Memcached, etc. See the `Data Stores` section below.
+	// store: ... , // Redis, Memcached, etc. See below.
 })
 
 // Apply the rate limiting middleware to all requests.