docs(comments): add some comments

this is the subject of the commit

pkg/notify/slack.go

@@ -1,3 +1,4 @@
+// Package notify provides a simple interface to send notifications to Slack.
 package notify
 
 import (
@@ -14,6 +15,7 @@ import (
 	"terminalShop/pkg/models"
 )
 
+// slack client
 var slackClient = &http.Client{Timeout: 5 * time.Second}
 
 // dollars converts cents to dollars