doc: clarify that Postgres v11 or higher is required
See golang/go#43154, where an older version was missing a function we
use.
Trust: Jonathan Amsterdam
Run-TryBot: Jonathan Amsterdam
TryBot-Result: kokoro
@@ -8,8 +8,8 @@ For additional information on our architecture, see the
## Local development database
-1. Install PostgreSQL on your machine for local development.
- It should use the default Postgres port of 5432.
+1. Install PostgreSQL (version 11 or higher) on your machine for local
+ development. It should use the default Postgres port of 5432.
If you use a Mac, the easiest way to do that is through installing
https://postgresapp.com.
