Merge pull request #2 from darmen/master

Update readme.md

Author: wataridori

readme.md

@@ -1,18 +1,23 @@
 ## SOLID Principles Examples in PHP
 
-### Single Responsibility Principle
-A class should have one, and only one, reason to change. [Example](./1-single-responsibility-principle.php)
+### Single Responsibility Principle ([Example](./1-single-responsibility-principle.php))
+This principle is about **actors and high level architecture**.
+> A class should have one, and only one, reason to change.
 
-### Open Closed Principle
-A class should be open for extension, but closed for modification. [Example](./2-open-closed-principle.php)
+### Open Closed Principle ([Example](./2-open-closed-principle.php))
+This principle is about **class design and feature extensions**.
+> A class should be open for extension, but closed for modification.
 
-### Liskov Substitution Principle
-Derived classes must be substitutable for their base classes. [Example](./3-liskov-substitution-principle.php)
+### Liskov Substitution Principle ([Example](./3-liskov-substitution-principle.php))
+This principle is about **subtyping and inheritance**
+> Derived classes must be substitutable for their base classes.
 
-### Interface Segregation Principle
-Many client-specific interfaces are better than one general-purpose interface. [Example](./4-interface-segregation-principle.php)
+### Interface Segregation Principle ([Example](./4-interface-segregation-principle.php))
+This principle is about **business logic to clients communication**.
+> Many client-specific interfaces are better than one general-purpose interface.
 
-### Dependency Inversion Principle
-Depend upon abstractions. Do not depend upon concretions. [Example](./5-dependency-inversion-principle.php)
+### Dependency Inversion Principle ([Example](./5-dependency-inversion-principle.php))
+> This principle wires up all **other four principles in a single circle**.
+Depend upon abstractions. Do not depend upon concretions.
 
 #### For more information about *Object Oriented Design Principles*, you can refer [this slide](https://viblo.asia/thangtd90/posts/pVYRPJPmG4ng)