UG -> Getting Started: Make this section more user friendly

[damithc]

As this is the first page new users will read, we should try to make it as beginner-friendly as possible.

Suggestions:

• This note seems a bit 'too technical' for someone just getting started with MarkBind.
  
  Either rephrase to be friendlier, or move somewhere else?

• We can provide more guidance on how to install npm+node etc. For example, for each OS, we can point to which page to go to and which version to install.

[lhw-1]

In terms of the Node LTS Error message, we can move the bulk of the comment (and maybe a bit more details from the GitHub issue, instead of just linking the issue itself) to the "Troubleshooting" section. We can also truncate this current comment and link the "Troubleshooting" subsection on the error directly.

In terms of guidance on npm and node installation, as @damithc suggested, linking the npm and node installation pages for each of the supported OSes should be sufficient. We could even display the links in a table format (or some other component that could be used here, at the discretion of whoever wants to try tackling this issue 😄).

[seah-minlong]

For the Node LTS Error, the documentation for the warning seems to have been removed in the code following PR #2572, but the website has not been updated to reflect this change yet 😄.