feat: include a warning about generated files when generating files 💪

I recently landed myself in an `id_gen.go` file using IDE's Go To Definition and started making updates, not noticing that it was a generated file.

This preamble would probably not help me because the file was long but perhaps it will help someone else. 🤷‍♂️

CHANGELOG.md

@@ -4,6 +4,8 @@ How to release a new version:
 - Manually release new version.
 
 ## [Unreleased]
+### Added
+- `gen_id` now includes a comment at the top of the generated file to warn developers that the file is, in fact, generated.
 
 ## [0.4.0] - 2023-03-27
 ### Added

cmd/tea/gen_id.go

@@ -18,6 +18,7 @@ import (
 )
 
 var (
+	outputPreamble = "// Code generated by tea. DO NOT EDIT.\n\n"
 	// genIDCmd represents the id command
 	genIDCmd = &cobra.Command{
 		Use:   "id",
@@ -141,6 +142,10 @@ func (i IDs) generate() ([]byte, error) {
 	var genData []byte
 	var err error
 
+	if _, err = output.WriteString(outputPreamble); err != nil {
+		return nil, fmt.Errorf("writing output preamble: %w", err)
+	}
+
 	for typ := range i {
 		//nolint:gocritic,exhaustive
 		switch typ {