config: improve config v1 deprecation message

The previous wording was causing confusion.
Fix moby/moby issue 43628

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>
(cherry picked from commit 739cb4c)
Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

services/server/config/config.go

@@ -97,7 +97,8 @@ func (c *Config) GetVersion() int {
 func (c *Config) ValidateV2() error {
 	version := c.GetVersion()
 	if version < 2 {
-		logrus.Warnf("deprecated version : `%d`, please switch to version `2`", version)
+		logrus.Warnf("containerd config version `%d` has been deprecated and will be removed in containerd v2.0, please switch to version `2`, "+
+			"see https://github.com/containerd/containerd/blob/main/docs/PLUGINS.md#version-header", version)
 		return nil
 	}
 	for _, p := range c.DisabledPlugins {