Added content to Angular SSG (#2323)

* Added content to readme.md file in 114-angular-ssg

[#1847 ](https://github.com/kamranahmedse/developer-roadmap/issues/1847) I added the required content to the readme.md file in 114-angular-ssg folder to resolve the issue.

* Update content/roadmaps/104-angular/content/114-angular-ssg/readme.md

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

content/roadmaps/104-angular/content/114-angular-ssg/readme.md

@@ -1 +1,3 @@
-# Angular ssg
+# Angular SSG
+
+SSG (Static Site Generator), helps in building the HTML full website, during the process of building and serving that HTML Page. This method helps to generate the HTML website on the client side before its being served on the server side. Therefore, whenever a user requests a HTML Page, firstly HTML page will be rendered and secondly, the angular app will be rendered. The SSG can be used only if your website is static (or) it's content doesn't changes frequently.