adding "solid-principle" (#35663)

* adding "solid-principle"

* added title for front matter block

* Update guide/english/design-patterns/solid-principle/index.md

Co-Authored-By: yoadwo <yoadw20@gmail.com>

guide/english/design-patterns/solid-principle/index.md

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+---
+title: SOLID Principle
+---
+## SOLID Principle
+
+A key programming princple which consists of the following conventions:
+(S)ingle Responsibility Principle
+(O)pen/Closed Principle
+(L)iskov Substitution Principle
+(I)nterface Segregation Principle
+(D)ependency Inversion
+
+Solid Responsibilty means a class should only do one thing (and preferably, do it well). So if a class is currently 
+interacting with some SQL database, and also can generate a HTML page from them - the two functionalities should be seperated. 
+
+Open/Closed Principle means you two never modify an existing class, but rather to extend them (does the word 'inheritance' ring
+any bells for you?).
+
+Liskov Substitution is one most often ignored. It means that whenever a code is written with use of base and child classes,
+it should be written as such that the program will never crash even if the child classes are substituted with their parent's.
+Suppose we have an Animal base class and a Dog\Cat child classes: It should not harm the flow if we write every Dog instance with
+an Animal's.
+
+ Interface Segregation Principle means that when writing interfaces, it is better to write many ones each with very particular
+ purpose, rather than having one interface to rule them all. Programmers are more likely to reuse small ones, and programs will
+ be less cloggy with having to implement a big one.
+ 
+ Dependency Inversion Principle means in (very) short, dont depend on concrete classes; try to use interfaces more.