Description and resources for SOLID (#1021)

Add a description and resources for the SOLID design principles

content/roadmaps/101-backend/content/114-design-and-development-principles/103-solid.md

@@ -1 +1,15 @@
-# Solid
+# SOLID
+
+SOLID is a set of principles applied to object-oriented design (OOD) to create maintainable, understandable, and flexible code, while avoiding code smells and defects. The principles are:
+
+- Single Responsibility
+- Open/Closed
+- Liskov Substitution
+- Interface Segregation
+- Dependency Inversion
+
+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+<BadgeLink colorScheme='blue' badgeText='Original Paper' href='https://web.archive.org/web/20150906155800/http://www.objectmentor.com/resources/articles/Principles_and_Patterns.pdf'>Design Principles and
+Design Patterns</BadgeLink>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://www.baeldung.com/solid-principles'>SOLID Principles</BadgeLink>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://www.digitalocean.com/community/conceptual_articles/s-o-l-i-d-the-first-five-principles-of-object-oriented-design'>SOLID: The First 5 Principles of Object Oriented Design</BadgeLink>