custom nodes: update to work with latest eclair

[halseth]

Updates instructions for how to build custom eclair image to work with latest version.

The other Dockerfile probably also needs update. And the config option

 --on-chain-fees.max-feerate-mismatch=100000

should now be

  --on-chain-fees.feerate-tolerance.ratio-low=0.00001
  --on-chain-fees.feerate-tolerance.ratio-high=10000.0

[codecov-io]

Codecov Report

Merging #390 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #390   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          113       113           
  Lines         3245      3245           
  Branches       565       565           
=========================================
  Hits          3245      3245           

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[jamaljsr]

Wow! I was expecting the diff to be much larger. I'll test it out myself and merge if it's all good. Thanks so much for the PR.

[jamaljsr]

tACK 🚀

squashing to fix commit message