add correct link to pg.pool documentation page (brianc#89)

https://node-postgres.com/api/pool

Author: Nilegfx

content/features/3-pooling.mdx

@@ -17,7 +17,7 @@ The easiest and by far most common way to use node-postgres is through a connect
 
 ### Good news
 
-node-postgres ships with built-in connection pooling via the [pg-pool]() module.
+node-postgres ships with built-in connection pooling via the [pg-pool](/api/pool) module.
 
 ## Examples