Update README.md (#2245)
Update README.md (#2245)

Move the `alertmanager.url` to a new line.

Signed-off-by: Razique Mahroua <7e21e97a73148ff77fd68e82d8890c7cd1a9c32e@redhat.com>
prometheus/alertmanager,GoogleCloudPlatform/alertmanager,prometheus/alertmanager,GoogleCloudPlatform/alertmanager,GoogleCloudPlatform/alertmanager,prometheus/alertmanager,GoogleCloudPlatform/alertmanager,prometheus/alertmanager