cmd/proxy-to-grafana: fix package doc code snippet

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Change-Id: I8d9bb92260c164dc277afbce624f64fc2faf5125
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/proxy-to-grafana/proxy-to-grafana.go

@@ -14,16 +14,14 @@
 //
 // Use this Grafana configuration to enable the auth proxy:
 //
-// ```
+//     [auth.proxy]
-// [auth.proxy]
+//     enabled = true
-// enabled = true
+//     header_name = X-WEBAUTH-USER
-// header_name = X-WEBAUTH-USER
+//     header_property = username
-// header_property = username
+//     auto_sign_up = true
-// auto_sign_up = true
+//     whitelist = 127.0.0.1
-// whitelist = 127.0.0.1
+//     headers = Name:X-WEBAUTH-NAME
-// headers = Name:X-WEBAUTH-NAME
+//     enable_login_token = true
-// enable_login_token = true
-// ```
 package main
 
 import (