Add example of how to implement a POST request

[sonirico]

By "sniffing" the normal request (Page.navigate, GET method), method, headers and postData parameters can be modified. As this is not fairly intuitive, I decided to add an example.

[codecov[bot]]

Codecov Report

Merging #23 into master will decrease coverage by 0.47%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #23      +/-   ##
==========================================
- Coverage   93.36%   92.89%   -0.48%     
==========================================
  Files           4        4              
  Lines         211      211              
  Branches       21       21              
==========================================
- Hits          197      196       -1     
  Misses          7        7              
- Partials        7        8       +1

Impacted Files	Coverage Δ
pychrome/tab.py	90.78% <0%> (-0.66%)	:arrow_down:

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[fate0]

thanks