Correct the headers in README.md

[iProzd]

No description provided.

[codecov-commenter]

Codecov Report

Base: 82.35% // Head: 82.35% // No change to project coverage 👍

Coverage data is based on head (5d7fae0) compared to base (d622c95).
Patch has no changes to coverable lines.

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Additional details and impacted files

@@           Coverage Diff           @@
##            devel     #424   +/-   ##
=======================================
  Coverage   82.35%   82.35%           
=======================================
  Files          68       68           
  Lines        6182     6182           
=======================================
  Hits         5091     5091           
  Misses       1091     1091           

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[njzjz]

The previous header is correct. However, other headers are wrong. In a doc, there should be only one = title = (i.e. h1).

[iProzd]

The previous header is correct. However, other headers are wrong. In a doc, there should be only one = title = (i.e. h1).

Then maybe I also correct other headers in this PR?