Update caches.mdx (#1289)

src/docs/sdk/performance/modules/caches.mdx

@@ -15,12 +15,16 @@ The SDK's caching integration is agnostic to the underlying engine used. In most
 | `cache.remove` | A single item or multiple items are removed from the cache |
 | `cache.flush` | The entire content of the cache is deleted |
 
+### Span Description
+
+The description of cache spans should be set to the cache key(s), sepreated by commas, e.g. `posts`, or `article1, article2`.
+
 ### Span Data
 
 | Data Key | Type | Description | Conditions
 |:--|:--|:--|:--|
 | `cache.hit` | bool | cache hit or miss | required only on read-operations (`cache.get`)
-| `cache.key ` | array | the key(s) involved in the operation | required only on operations that have a key
+| `cache.key` | array | the key(s) involved in the operation | required only on operations that have a key
 
 The following data attributes are only to be set if exposed by the instrumented cache abstraction or retrievable with minimal overhead.