FMWK-651 Update documentation and improve test coverage

[filkeith]

• reworked readme
• reworked readers

test coverage will be increased in separate task, when I'll finish adding new functionality.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 66.66667% with 37 lines in your changes missing coverage. Please review.

Project coverage is 78.54%. Comparing base (d6bfe30) to head (c7fd452).

Files with missing lines	Patch %	Lines
io/aws/s3/reader.go	57.69%	8 Missing and 3 partials ⚠️
io/azure/blob/reader.go	61.53%	6 Missing and 4 partials ⚠️
io/gcp/storage/reader.go	61.53%	6 Missing and 4 partials ⚠️
io/local/reader.go	70.58%	3 Missing and 2 partials ⚠️
internal/util/files_sort.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           xdr-support     #212      +/-   ##
===============================================
- Coverage        78.57%   78.54%   -0.04%     
===============================================
  Files              110      110              
  Lines            10079     9941     -138     
===============================================
- Hits              7920     7808     -112     
+ Misses            1661     1635      -26     
  Partials           498      498              

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