bump version 1.3 to 1.4 in README

[awaelchli]

What does this PR do?

Also created a branch release/1.4.x

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[codecov]

Codecov Report

Merging #8582 (f3377ea) into master (39de7fe) will decrease coverage by 0%.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #8582   +/-   ##
======================================
- Coverage      92%     92%   -0%     
======================================
  Files         218     218           
  Lines       14411   14480   +69     
======================================
+ Hits        13307   13322   +15     
- Misses       1104    1158   +54