Add instructions for installing GStreamer

[aksell]

Description

Closes #38

Short description of what this resolves:

Add installation instructions for MacOS, Windows and Linux

Checklist before merging

• [x] Run the tests while connected to a drone

I think this should be squashed before it is merged

[codecov[bot]]

Codecov Report

Merging #43 into master will increase coverage by 0.02%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #43      +/-   ##
==========================================
+ Coverage   46.36%   46.38%   +0.02%     
==========================================
  Files           5        5              
  Lines         261      263       +2     
==========================================
+ Hits          121      122       +1     
- Misses        140      141       +1

Flag	Coverage Δ
#macos	46.38% <ø> (+0.02%)	:arrow_up:
#ubuntu	46.38% <ø> (+0.02%)	:arrow_up:
#windows	46.38% <ø> (+0.02%)	:arrow_up:

Impacted Files	Coverage Δ
blueye/sdk/diagnostics.py	0% <0%> (ø)	:arrow_up:
blueye/sdk/pioneer.py	66.66% <0%> (+0.38%)	:arrow_up:

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