Instruct to create annotated tags

[pnuu]

Simple addition to release instructions, where git tag -a needs to be used so that git push --follow-tags will work.

[codecov]

Codecov Report

Merging #40 (0d0fd69) into main (70a3a0d) will decrease coverage by 0.45%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main      #40      +/-   ##
==========================================
- Coverage   80.81%   80.36%   -0.46%     
==========================================
  Files          15       15              
  Lines        1991     1991              
==========================================
- Hits         1609     1600       -9     
- Misses        382      391       +9     

Impacted Files	Coverage Δ
posttroll/version.py	41.57% <0.00%> (-3.23%)	⬇️

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[mraspaud]

LGTM