Howdy Jiban! Thank you for posting about this!
My main suggestion for improving the on-boarding process and documentation is to possible improve traceability / discoverability of related Ignition (and possibly ROS1/2) packages, mainly through some sort of categorized index of packages.
FTR, the Ignition > Libraries page has a start, but the “Details” section is a bit sparse in some of the packages, and some packages (e.g. SDFormat 
) may be missing.
The most relevant (but a bit narrowly scoped) issue is https://github.com/osrf/sdf_tutorials/issues/2 - having specific links from each repository’s README, saying what its scope is, etc.
I’ve posted some relevant ROS issues as well there.
Meta Question:
Might I ask if you’d like me to put these suggestions anywhere else? Is here on Gazebo Community good, or would you like it as a comment on your Google Doc?
For my background:
I am part of Toyota Research Institute (TRI) and am working with @scpeters and @azeey on some aspects of SDFormat Development, currently working towards this “epic”:
https://github.com/osrf/sdformat/issues/278
Our overarching goal is catered towards (a) refining the SDFormat documentation (such that the spec is standalone, rather than implicit in libsdformat code / Gazebo tutorials / Gazebo code) and (b) leveraging the documentation of existing behavior to then propose new functionality for SDFormat.
(I would post a link, but I’m limited to 2 
)