docs: fix markdown lint issues in command docs

cmd/selfupdate/selfupdate.go

@@ -65,7 +65,7 @@ var cmdSelfUpdate = &cobra.Command{
 	Use:     "selfupdate",
 	Aliases: []string{"self-update"},
 	Short:   `Update the rclone binary.`,
-	Long:    selfUpdateHelp,
+	Long:    strings.TrimSpace(selfUpdateHelp),
 	Annotations: map[string]string{
 		"versionIntroduced": "v1.55",
 	},

cmd/selfupdate/selfupdate.md

@@ -43,5 +43,5 @@ command will rename the old executable to 'rclone.old.exe' upon success.
 
 Please note that this command was not available before rclone version 1.55.
 If it fails for you with the message `unknown command "selfupdate"` then
-you will need to update manually following the install instructions located
-at https://rclone.org/install/
+you will need to update manually following the
+[install documentation](https://rclone.org/install/).