add link to PR

Author: bwengals

RELEASE-NOTES.md

@@ -45,7 +45,7 @@ All of the above apply to:
 - Changes to the BART implementation:
   - A BART variable can be combined with other random variables. The `inv_link` argument has been removed (see [4914](https://github.com/pymc-devs/pymc3/pull/4914)).
   - Moved BART to its own module (see [5058](https://github.com/pymc-devs/pymc3/pull/5058)).
-- Changes to the Gaussian Process (GP) submodule:
+- Changes to the Gaussian Process (GP) submodule (see [5055](https://github.com/pymc-devs/pymc/pull/5055)):
   - For all implementations, `gp.Latent`, `gp.Marginal` etc., `cov_func` and `mean_func` are required kwargs.
   - In Windows test conda environment the `mkl` version is fixed to verison 2020.4, and `mkl-service` is fixed to `2.3.0`.  This was required for `gp.MarginalKron` to function properly.
   - `gp.MvStudentT` uses rotated samples from `StudentT` directly now, instead of sampling from `pm.Chi2` and then from `pm.Normal`.