Grammar - Add missing 'and' (#2491)

Author: jamiegs

commands/memory-usage.md

@@ -2,7 +2,7 @@ The `MEMORY USAGE` command reports the number of bytes that a key and its value
 require to be stored in RAM.
 
 The reported usage is the total of memory allocations for data and
-administrative overheads that a key its value require.
+administrative overheads that a key and its value require.
 
 For nested data types, the optional `SAMPLES` option can be provided, where
 `count` is the number of sampled nested values. The samples are averaged to estimate the total size.