Rely on the PR template for docs/code consistency [#12]

These comments were a reasonable attempt at ensuring the documentation
matched reality, but the checkbox in the pull request template is much
more likely to produce results.

internal/run/upgrade.go

@@ -25,8 +25,6 @@ func (u *Upgrade) Execute(_ Config) error {
 }
 
 // Prepare gets the Upgrade ready to execute.
-// Note: mandatory settings are documented in README.md, and the full list of settings is in docs/upgrade_settings.yml.
-// Any additions or deletions here should be reflected there.
 func (u *Upgrade) Prepare(cfg Config) error {
 	if u.Chart == "" {
 		return fmt.Errorf("chart is required")