Add WebSocket client example to README

[jpsamaroo]

Follow up of #96

[codecov-io]

Codecov Report

Merging #97 into master will decrease coverage by 7.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #97      +/-   ##
==========================================
- Coverage   54.01%   46.96%   -7.05%     
==========================================
  Files           7        7              
  Lines         137      132       -5     
==========================================
- Hits           74       62      -12     
- Misses         63       70       +7

Impacted Files	Coverage Δ
src/Mux.jl	50% <0%> (-27.78%)	⬇️
src/examples/files.jl	7.4% <0%> (-18.52%)	⬇️
src/routing.jl	71.87% <0%> (-3.89%)	⬇️
src/basics.jl	71.87% <0%> (+0.44%)	⬆️

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