Correct typos and formatting in README

[RayStick]

I was reading the README file and noticed a typo, so I corrected it. Then also made a few minor formatting improvements. I did them each as separate commits if we only want to accept some of them.

Proposed Changes

1. I corrected a spelling mistake (Subsistems -> Subsystems)
2. The line that starts "We want to offer as much support as possible ..." was on the same line as the GE bullet point but it looked like it was meant to be on a separate line
3. Some suggested re-wording to the 'Tested OSs' section - there were no mistakes here though, so just improvements.

Change Type

• [ ] bugfix (+0.0.1)
• [ ] minor (+0.1.0)
• [ ] major (+1.0.0)
• [ ] refactoring (no version update)
• [ ] test (no version update)
• [ ] infrastructure (no version update)
• [x] documentation (no version update). I assume this is the right one to tick as README is essentially documentation? Or is this label just for files in /docs?
• [ ] other

Checklist before review

• [x] I added everything I wanted to add to this PR.
• [ ] [Code or tests only] I wrote/updated the necessary docstrings. N/A
• [ ] [Code or tests only] I ran and passed tests locally. N/A
• [ ] [Documentation only] I built the docs locally. N/A as this is just for /docs ?
• [x] My contribution is harmonious with the rest of the code: I'm not introducing repetitions.
• [ ] My code respects the adopted style, especially linting conventions. N/A
• [x] The title of this PR is explanatory on its own, enough to be understood as part of a changelog.
• [x] I added or indicated the right labels.

• [ ] I added information regarding the timeline of completion for this PR. N/A

• [x] Please, comment on my PR while it's a draft and give me feedback on the development!

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (91ddcef) 91.18% compared to head (0f6bd72) 91.18%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #463   +/-   ##
=======================================
  Coverage   91.18%   91.18%           
=======================================
  Files           8        8           
  Lines        1010     1010           
=======================================
  Hits          921      921           
  Misses         89       89           

[RayStick]

@smoia I requested you as reviewer (should be a quick review) but if you prefer - please request someone else that would be good to review it and then remove yourself