[documentation] Add comments in krylov_solve.jl

[amontoison]

close #915

[codecov]

Codecov Report

Attention: Patch coverage is 71.42857% with 10 lines in your changes missing coverage. Please review.

Project coverage is 94.67%. Comparing base (d1215ab) to head (887d3eb).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/krylov_solve.jl	71.42%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #919      +/-   ##
==========================================
+ Coverage   94.17%   94.67%   +0.50%     
==========================================
  Files          45       45              
  Lines        8219     8229      +10     
==========================================
+ Hits         7740     7791      +51     
+ Misses        479      438      -41     

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[github-actions]

Package name	latest	stable
CaNNOLeS.jl
DCISolver.jl
FletcherPenaltySolver.jl
JSOSolvers.jl
LLSModels.jl
LinearSolve.jl
Percival.jl
RipQP.jl