Fix typo in README (#272)

Fix typo

Author: eoinkelly

README.md

@@ -188,7 +188,7 @@ We use the `PARTITION BY HASH` hashing function, the same as used by Postgres fo
 To route queries to a particular shard, we use this custom SQL syntax:
 
 ```sql
--- To talk to a shard explicitely
+-- To talk to a shard explicitly
 SET SHARD TO '1';
 
 -- To let the pooler choose based on a value