docs: update the installation guide

[emrahcom]

• Delete the notes that are no longer valid and replace them with the current working way.
• Format the markdown text

[jitsi-jenkins]

Hi, thanks for your contribution!
If you haven't already done so, could you please make sure you sign our CLA (https://jitsi.org/icla for individuals and https://jitsi.org/ccla for corporations)? We would unfortunately be unable to merge your patch unless we have that piece :(.

[codecov]

Codecov Report

Merging #518 (0085f35) into master (689aadf) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #518   +/-   ##
=========================================
  Coverage     48.17%   48.17%           
  Complexity      174      174           
=========================================
  Files            72       72           
  Lines          2113     2113           
  Branches        201      201           
=========================================
  Hits           1018     1018           
  Misses         1027     1027           
  Partials         68       68           

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[saghul]

🙏