slightly change the CONTRIBUTING.md and the changelog, for the new release

Author: BDonnot

CHANGELOG.rst

@@ -66,7 +66,7 @@ Next release
 - TODO work on the reward class (see https://github.com/rte-france/Grid2Op/issues/584)
 
 
-[1.10.4] - 2024-xx-yy
+[1.10.4] - 2024-10-14
 -------------------------
 - [FIXED] an issue in the backend: if the backend failed to be
   created the `_grid` attribute was set to `None` and not set back to
@@ -84,6 +84,7 @@ Next release
 - [ADDED] numpy 2 support (now that pandapower allows it)
 - [IMPROVED] error message when forecasts are not correctly set-up
 
+
 [1.10.3] - 2024-07-12
 -------------------------
 - [BREAKING] `env.chronics_hander.set_max_iter(xxx)` is now a private function. Use 

CONTRIBUTING.md

@@ -49,4 +49,7 @@ get in touch with the team)
 Code in the contribution should pass all the current tests, have some dedicated tests for the new feature (if applicable)
 and documentation (if applicable).
 
+If you contribute to some grid2op notebooks, please make sure to "clear all outputs"
+before making the pull request.
+
 New contributions should respect the "**Code of Conduct**" of grid2op.