add intro

Author: sarven

README.md

@@ -1,5 +1,14 @@
 # [Work in progress] Unit testing tips by examples in PHP
 
+## Introduction
+
+In these times the benefits of writing unit tests are huge.
+I think that most of the recently started projects contain any unit tests.
+In enterprise applications with a lot of business logic, unit tests are the most important tests,
+because they are fast and can us instantly assure that our implementation is correct.
+However, I often see a problem with good tests in projects, though the benefits of these tests are only huge when you have good unit tests.
+So in these examples, I will try to share some tips on what to do to write good unit tests.
+
 ## Table of Contents
 
 1. [Introduction](#introduction)