Add Windows installation

[mabelzhang]

Partially addresses gazebosim/docs#117

Made headings and code blocks consistent with other per-package installation tutorials.

[codecov]

Codecov Report

Merging #33 (b5b4d3f) into main (a700c15) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##              main       #33   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           14        14           
  Lines          554       554           
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  Hits           554       554           

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[JShep1]

This is a general comment moreso about all of the build/installation tutorials.

I noticed there's less consistency among all of these (ie, ign transport tutorials are organized by binary and source and then subdivided into the OS, ign msgs tutorials have UNIX vs. Windows as opposed to explicitly listing Ubuntu vs macOS vs Windows and also have a Dependencies and Installation section, etc.). I feel like while we're here we should probably establish a unified format and update all of the installation tutorials to abide by it.

I think I personally like sorting by OS and then under the OS have the type of desired installation, but honestly don't think there's a tremendous difference.

[mabelzhang]

Closing in favor of #34
Standardized format there. (Edit: looks like I have something from before to copy-paste for the nesting requested. No guarantee about other libs before this one though. I've been committing a ton of nits to all the previous PRs to keep things consistent. I'm not confident things will remain consistent after 6 months 😅 )