Clarify need for connect_timeout in the DSN

Add connect_timeout to the examples and clarify why this is a good idea
in the README: database/sql may open new connections asynchronously so
it doesn't use the context from QueryContext(), PingContext(), etc.

This makes sense, but is somewhat unexpected.

Fixes #1020

Author: arp242

README.md

@@ -22,7 +22,7 @@ import (
 
 func main() {
     // Or as URL: postgresql://localhost/pqgo
-    db, err := sql.Open("postgres", "host=localhost dbname=pqgo")
+    db, err := sql.Open("postgres", "host=localhost dbname=pqgo connect_timeout=5")
     if err != nil {
         log.Fatal(err)
     }
@@ -42,9 +42,10 @@ You can also use the `pq.Config` struct:
 
 ```go
 cfg := pq.Config{
-    Host: "localhost",
-    Port: 5432,
-    User: "pqgo",
+	Host:           "localhost",
+	Port:           5432,
+	User:           "pqgo",
+	ConnectTimeout: 5 * time.Second,
 }
 // Or: create a new Config from the defaults, environment, and DSN.
 // cfg, err := pq.NewConfig("host=postgres dbname=pqgo")
@@ -85,6 +86,10 @@ The libpq way (which also works in pq) is to use `options='-c k=v'` like so:
 
     sql.Open("postgres", "dbname=pqgo options='-c work_mem=100kB -c search_path=xyz'")
 
+It's recommended to add `connect_timeout` to the DSN – database/sql may open new
+connections asynchronously so it doesn't use the context from QueryContext(),
+PingContext(), etc. The default is to wait indefinitely.
+
 [Config struct]: https://pkg.go.dev/github.com/lib/pq#Config
 [run-time parameter]: http://www.postgresql.org/docs/current/static/runtime-config.html
 

doc.go

@@ -11,7 +11,7 @@ directly. For example:
 	)
 
 	func main() {
-		dsn := "user=pqgo dbname=pqgo sslmode=verify-full"
+		dsn := "user=pqgo dbname=pqgo sslmode=verify-full connect_timeout=5"
 		db, err := sql.Open("postgres", dsn)
 		if err != nil {
 			log.Fatal(err)
@@ -24,7 +24,7 @@ directly. For example:
 
 You can also connect with an URL:
 
-	dsn := "postgres://pqgo:password@localhost/pqgo?sslmode=verify-full"
+	dsn := "postgres://pqgo:password@localhost/pqgo?sslmode=verify-full&connect_timeout=5"
 	db, err := sql.Open("postgres", dsn)
 
 # Connection String Parameters