Add documentation for triagebot new_draft option for autolabels

Author: Urgau

src/triagebot/autolabels.md

@@ -57,7 +57,7 @@ exclude_labels = [
 
 ### Triggered by new PRs
 
-Labels can be added to any PR when it is opened.
+Labels can be added to any PR when it is opened as non-draft.
 Set the `new_pr = true` config option to enable this.
 For example:
 
@@ -66,6 +66,17 @@ For example:
 new_pr = true
 ```
 
+### Triggered by new draft PRs
+
+Labels can be added to any PR when it is opened as draft.
+Set the `new_draft = true` config option to enable this.
+For example:
+
+```toml
+[autolabel."S-waiting-on-author"]
+new_draft = true
+```
+
 ### Triggered by new issues
 
 Labels can be added to any issue when it is opened.