antool: add README.md

[ldorau]

This change is 

[codecov[bot]]

Codecov Report

Merging #427 into master will decrease coverage by 0.19%. The diff coverage is n/a.

@@            Coverage Diff            @@
##           master     #427     +/-   ##
=========================================
- Coverage   76.16%   75.96%   -0.2%     
=========================================
  Files          70       70             
  Lines        8805     8805             
  Branches     1779     1779             
=========================================
- Hits         6706     6689     -17     
- Misses       1607     1626     +19     
+ Partials      492      490      -2

Flag	Coverage Δ
#ltp_tests	44.77% <ø> (-0.25%)	:arrow_down:
#sqlite_tests	44.89% <ø> (-0.08%)	:arrow_down:
#tests_antool	15.06% <ø> (ø)	:arrow_up:
#tests_posix_multi_threaded	25.43% <ø> (+0.03%)	:arrow_up:
#tests_posix_single_threaded	53.45% <ø> (ø)	:arrow_up:
#tests_preload	44.42% <ø> (-0.09%)	:arrow_down:

Impacted Files	Coverage Δ
src/libpmemfile-posix/fcntl.c	46.91% <0%> (-16.05%)	:arrow_down:
src/libpmemfile/vfd_table.c	80.26% <0%> (-0.9%)	:arrow_down:
src/libpmemfile-posix/dir.c	85.53% <0%> (-0.5%)	:arrow_down:

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[krzycz]

Reviewed 1 of 1 files at r1. Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from Reviewable

[marcinslusarz]

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Reviewed 1 of 1 files at r2. Review status: all files reviewed at latest revision, all discussions resolved, some commit checks failed.

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Comments from Reviewable