Add information in README about discontinuation of the project

[szadam]

Preview: https://github.com/szadam/pmemkv/blob/master/README.md

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This change is 

[codecov]

Codecov Report

Merging #1087 (ab256e3) into master (f7cc6ed) will decrease coverage by 1.40%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1087      +/-   ##
==========================================
- Coverage   92.37%   90.97%   -1.40%     
==========================================
  Files          38       38              
  Lines        3802     3767      -35     
==========================================
- Hits         3512     3427      -85     
- Misses        290      340      +50     

Impacted Files	Coverage Δ
src/config.h	5.97% <0.00%> (-80.57%)	⬇️
src/exceptions.h	63.63% <0.00%> (-11.37%)	⬇️
src/comparator/pmemobj_comparator.h	85.71% <0.00%> (+3.89%)	⬆️

[lukaszstolarczuk]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @szadam)

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README.md line 32 at r1 (raw file):

Up-to-date, current support/maintenance status of branches/releases is available on
[pmem.io](https://pmem.io/pmemkv/index.html#releases-support-status).

pls drop this information about current support statuses - we'll drop that from the microsite

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README.md line 78 at r1 (raw file):

* **Python** - https://github.com/pmem/pmemkv-python
* **Ruby** - https://github.com/pmem/pmemkv-ruby

BTW, we have to do the same update on all these pmemkv-* repos

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README.md line 114 at r1 (raw file):

## Contact us
For more information about **pmemkv** contact us using dedicated email: pmdk_support@intel.com.

pls rather use a similar message to the one worked out in the pmemstream's PR

[szadam]

Reviewable status: 0 of 1 files reviewed, 3 unresolved discussions (waiting on @lukaszstolarczuk)

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README.md line 32 at r1 (raw file):

Previously, lukaszstolarczuk (Łukasz Stolarczuk) wrote…

pls drop this information about current support statuses - we'll drop that from the microsite

Done.

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README.md line 114 at r1 (raw file):

Previously, lukaszstolarczuk (Łukasz Stolarczuk) wrote…

pls rather use a similar message to the one worked out in the pmemstream's PR

I suggest sth like that.

[szadam]

Reviewable status: 0 of 1 files reviewed, 3 unresolved discussions (waiting on @lukaszstolarczuk)

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README.md line 114 at r1 (raw file):

Previously, szadam (Adam Szopiński) wrote…

I suggest sth like that.

done

[lukaszstolarczuk]

Reviewed 1 of 1 files at r3, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @szadam)