Update repo README with new wording, locust example, screenshots

[max-rocket-internet]

• Copy latest wording from docs
• Add very simple example that shows clearly how a locust file is written
• Add some screen shots from the UI
• Format features correctly using #### instead of bold bullet points
• Use consistent bullet point syntax
• Remove unnecessary HTML
• Add github links for authors
• Move Links to the end as these are boring
• Remove Documentation section as this is already in the Links section

[codecov]

Codecov Report

Merging #1532 into master will decrease coverage by 0.46%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1532      +/-   ##
==========================================
- Coverage   82.38%   81.91%   -0.47%     
==========================================
  Files          28       28              
  Lines        2560     2560              
  Branches      388      388              
==========================================
- Hits         2109     2097      -12     
- Misses        355      365      +10     
- Partials       96       98       +2     

Impacted Files	Coverage Δ
locust/clients.py	90.19% <0.00%> (-4.91%)	⬇️
locust/runners.py	83.23% <0.00%> (-1.34%)	⬇️

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[cyberw]

Thx!

[cyberw]

Huh. The images are broken on the pypi page: https://pypi.org/project/locust/

Perhaps we need to use absolute URLs to github (unless there is some other solution)

[max-rocket-internet]

OK I can make the image links use raw links to this repo