Fix link to CONTRIBUTING.md in README

Author: jgabry

README.md

@@ -62,7 +62,9 @@ CmdStanR_](https://mc-stan.org/cmdstanr/articles/cmdstanr.html) vignette.
 
 There is a lot of work still to be done, and we welcome contributions from
 anyone! If you are interested in contributing, please [comment on an open issue or
-open a new one](https://github.com/stan-dev/cmdstanr/issues) on GitHub. For more details, please check [CONTRIBUTING.md](https://github.com/stan-dev/cmdstanr/blob/fe126708f53d89ecd889d2f122f6bd69c7404836/.github/CONTRIBUTING.md).
+open a new one](https://github.com/stan-dev/cmdstanr/issues) on GitHub. For more details, 
+please check [CONTRIBUTING.md](.github/CONTRIBUTING.md).
+
 ### License
 
 CmdStanR, like CmdStan and the core Stan C++ code, is licensed under the