add docs on creating MIMO systems and arrays of systems

[baggepinnen]

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[JuliaControlBot]

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Plots were compared to references. 8/11 images have changed, see differences below.
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Difference	Reference Image	New Image
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[codecov]

Codecov Report

Merging #713 (9ef9794) into master (c624e1a) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #713      +/-   ##
==========================================
- Coverage   90.72%   90.70%   -0.03%     
==========================================
  Files          35       35              
  Lines        3710     3711       +1     
==========================================
  Hits         3366     3366              
- Misses        344      345       +1     

Impacted Files	Coverage Δ
src/types/StateSpace.jl	92.00% <0.00%> (-0.37%)	⬇️

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