add references to make getting started easier

[baggepinnen]

No description provided.

[JuliaControlBot]

This is an automated message.
Plots were compared to references. 8/11 images have changed, see differences below.
After pulling this PR, please update the reference images by creating a PR to ControlExamplePlots.jl here.

Difference	Reference Image	New Image
❌ 0.048
✔️ 0.0
✔️ 0.001
✔️ 0.001
✔️ 0.0
❌ 0.043
❌ 0.059
✔️ 0.01

[codecov]

Codecov Report

Merging #701 (e3442f2) into master (c2fa04b) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #701   +/-   ##
=======================================
  Coverage   87.88%   87.88%           
=======================================
  Files          35       35           
  Lines        3614     3614           
=======================================
  Hits         3176     3176           
  Misses        438      438           

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