Add ASCII ramp example to docs

[adrhill]

Adds the example shown in #61.

[codecov]

Codecov Report

Merging #64 (cdabd23) into master (2915ec4) will decrease coverage by 0.39%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #64      +/-   ##
==========================================
- Coverage   96.81%   96.41%   -0.40%     
==========================================
  Files          14       14              
  Lines         251      251              
==========================================
- Hits          243      242       -1     
- Misses          8        9       +1     

Impacted Files	Coverage Δ
src/utils.jl	57.14% <0.00%> (-14.29%)	⬇️

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