Readme update

[MichelMichels]

Following changes:

• Renamed LICENCE.md to LICENSE.md
• README.md
• Changed structure
• Added nuget shield
• Update code under 'Usage' to .NET 6
• Link to LICENSE.md instead of the full license copied in the readme
• Removed the statement that ImageSharp is in alpha state
• Update ImageSharp repo url

[pamapa]

Nice work on top of README.md, maybe you can rebase once my MR #265 has been merged...

[MichelMichels]

Nice work on top of README.md, maybe you can rebase once my MR #265 has been merged...

Yes, I like your structure better than mine for the README.md. I'll overwrite the code snippet with the newer .NET 6 example if that's ok.

[MichelMichels]

I added my .NET 6 example into the recently updated README.md.

[codecov-commenter]

Codecov Report

Merging #266 (9146b11) into master (2828a90) will increase coverage by 0.00%. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #266   +/-   ##
=======================================
  Coverage   26.62%   26.63%           
=======================================
  Files         238      238           
  Lines       23336    23336           
  Branches     2809     2809           
=======================================
+ Hits         6214     6216    +2     
+ Misses      16629    16628    -1     
+ Partials      493      492    -1     

Impacted Files	Coverage Δ
PdfSharpCore/Fonts/FontFactory.cs	35.25% <0.00%> (+1.28%)	:arrow_up:

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