Improve ReadMe

[maxbachmann]

The current readme does not reflect many of the most recent changes. It would make sense to update it accordingly:

• From the current readme it appears like rapidfuzz is a replacement for fuzzywuzzy. However rapidfuzz provides a growing number of features which are not supported by fuzzywuzzy like
  • more string metrics (e.g. levenshtein/hamming/jaro/jaro winkler
  • cdist
  • multithreading
    This should both be visible in the Description and in the Usage section
• The readme mentions installation from pip/conda/git. It would probably be enough to mention the installation via pip, since it is the most used version. For other versions the documentation could be referenced: https://maxbachmann.github.io/RapidFuzz/installation.html
• The usage section is relatively useless so far, since it only shows some arbitrary api calls without any explanation
• The benchmark section does not show very useful results, since it only shows a comparision between rapidfuzz and fuzzywuzzy for some arbitrary string lengths. I am not sure yet how to make this more usefull. Detailed benchmarks of each function are already included in the documentation.