Gazebo documentation index

The Gazebo project has a vast set of learning resources in the form of a documentation section, Gazebo tutorials, the QA website, ROS answers and other blogs that developers can refer to for any assistance. All of this information is distributed across the internet with some links joining each other. The aim of this project is to bring all the learning material under one webpage in the form of a documentation index that contains links to the content where the respective information is hosted. Almost all relevant information in such documentation indexes is just a page quick-search away. Such a platform can act as a one-stop place to get all pertinent information about Gazebo. A roadmap has been provided towards the end of the proposal to share information about how the project can be approached and developed in a planned fashion.