add info about key's limit

README.md

@@ -3,11 +3,11 @@
 
 The library adds a thin layer on top of [lru cache](https://github.com/hashicorp/golang-lru) and [patrickmn/go-cache](https://github.com/patrickmn/go-cache).
 
-| Cache name       | Constructor             | Defaults          | Description           |
-| ---------------- | ----------------------- | ----------------- | --------------------- |
-| `LruCache`       | `lcw.NewLruCache`       | keys=1000         | LRU cache with limits |
-| `ExpirableCache` | `lcw.NewExpirableCache` | keys=1000, ttl=5m | TTL cache with limits |
-| `Nop`            | `lcw.NewNopCache`       |                   | Do-nothing cache      |
+| Cache name     | Constructor           | Defaults          | Description           |
+| -------------- | --------------------- | ----------------- | --------------------- |
+| LruCache       | lcw.NewLruCache       | keys=1000         | LRU cache with limits |
+| ExpirableCache | lcw.NewExpirableCache | keys=1000, ttl=5m | TTL cache with limits |
+| Nop            | lcw.NewNopCache       |                   | Do-nothing cache      |
 
 
 Main features:
@@ -16,6 +16,7 @@ Main features:
 - Limit maximum cache size (in bytes)
 - Limit maximum key size
 - Limit maximum size of a value 
+- Limit number of keys
 - TTL support (`ExpirableCache` only)
 - Functional style invalidation
 - Functional options