Added content angular-obsevable-pattern (#2244)

* Added content angular-obsevable-pattern

* Update content/roadmaps/104-angular/content/101-rxjs-basics/100-observable-pattern.md

Co-authored-by: Kamran Ahmed <kamranahmed.se@gmail.com>

content/roadmaps/104-angular/content/101-rxjs-basics/100-observable-pattern.md

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-# Observable pattern
+# Observable Pattern
+
+The observer pattern is a software design pattern in which an object, named the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods.
+
+Angular uses the Observer pattern which simply means — Observable objects are registered, and other objects observe (in Angular using the subscribe method) them and take action when the observable object is acted on in some way.
+
+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+<BadgeLink badgeText='Read' colorScheme='yellow' href='https://medium.com/fuzzycloud/angular-and-observable-4bf890b2a282'>Angular and Observable</BadgeLink>