Update README.md

Finally remove old link to project proposal.

Author: bgroenks96

README.md

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 A partial implementation of the CryoGrid permafrost model in Julia, with a focus on parameter estimation and uncertainty quantification.
 
-Part of the broader research project: [Quantifying and explaining uncertainty in permafrost modeling under a warming climate](https://drive.google.com/file/d/1wB_EXtlO_PMXFSzZ-bRV8cg0a0DGDtAB/view?usp=sharing)
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 Author: Brian Groenke ([email protected])
 
 ## Key features