add release notesy

Author: Intron7

docs/release-notes/0.13.6.md

@@ -3,3 +3,7 @@
 ```{rubric} Features
 ```
 * Adds `ptg.Distance` for GPU-accelerated distance computation between groups of cells, compatible with pertpy's Distance API {pr}`454` {smaller}`S Dicks & S Özleyen`
+
+```{rubric} Misc
+```
+* RAPIDS nightly test success is no longer required for merging {pr}`539` {smaller}`S Dicks`