chore: wording in UPGRADING.md

Author: Luca Bianconi

docs/UPGRADING.md

@@ -4,6 +4,14 @@ Here you can find a list of migration guides to handle breaking changes between
 
 ## 0.30.0
 
+### Sketch name validation
+
+The sketch name submitted via the `sketch new` command of the CLI or the gRPC command
+`cc.arduino.cli.commands.v1.NewSketch` are now validated. The applied rules follow the
+[sketch specifications](https://arduino.github.io/arduino-cli/dev/sketch-specification).
+
+Existing sketch names violating the new constraints need to be updated.
+
 ### `daemon` CLI command's `--ip` flag removal
 
 The `daemon` CLI command no longer allows to set a custom ip for the gRPC communication. Currently there is not enough