Readiness callback and readme improvements

[alaneuler]

fix: #671
fix: #674

[glmapper]

LGTM

[codecov-commenter]

Codecov Report

Merging #675 into master will decrease coverage by 0.03%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #675      +/-   ##
============================================
- Coverage     51.21%   51.18%   -0.04%     
  Complexity       87       87              
============================================
  Files           276      276              
  Lines          7972     7977       +5     
  Branches       1128     1131       +3     
============================================
  Hits           4083     4083              
  Misses         3441     3441              
- Partials        448      453       +5     

Impacted Files	Coverage Δ	Complexity Δ
...lthcheck/AfterReadinessCheckCallbackProcessor.java	87.75% <100.00%> (+1.39%)	0.00 <0.00> (ø)
...m/alipay/sofa/isle/stage/ModuleLogOutputStage.java	84.76% <0.00%> (-3.81%)	0.00% <0.00%> (ø%)
...ime/component/impl/StandardSofaRuntimeManager.java	71.69% <0.00%> (-1.89%)	0.00% <0.00%> (ø%)

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