Update README.md

Created by: Ash-Crow

Fix issue #120 (replace outdated installation instructions with a link to the manual)

Created by: codecov-io

Current coverage is 91.34% (diff: 100%)

Merging #121 into master will not change coverage

@@             master       #121   diff @@
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  Files            52         52          
  Lines          1052       1052          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
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  Hits            961        961          
  Misses           91         91          
  Partials          0          0          

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