Added note on breaking API change

Author: cmaglie

Diff for: docs/UPGRADING.md

@@ -4,6 +4,23 @@ Here you can find a list of migration guides to handle breaking changes between
 
 ## Unreleased
 
+### `commands.Compile` function change
+
+A new argument `progressCB` has been added to `commands.Compile`, the new function signature is:
+
+```go
+func Compile(
+	ctx context.Context,
+	req *rpc.CompileRequest,
+	outStream, errStream io.Writer,
+	progressCB commands.TaskProgressCB,
+	debug bool
+) (r *rpc.CompileResponse, e error) {
+```
+
+if a callback function is provided the `Compile` command will call it periodically with progress reports with the
+percentage of compilation completed, otherwise, if the parameter is `nil`, no progress reports will be performed.
+
 ### `github.com/arduino/arduino-cli/cli/arguments.ParseReferences` function change
 
 The `parseArch` parameter was removed since it was unused and was always true. This means that the architecture gets