docs: updated release notes

Author: arshbot

release_notes.md

@@ -16,6 +16,15 @@ This file tracks release notes for the loop client.
 
 #### New Features
 
+* `--private` flag is now available on the `loop in` command, meaning users can
+  now loop in to private nodes! This was implemented in [#415](https://github.com/lightninglabs/loop/pull/415)
+  and has an implementation of LND's hop hints creation feature for the time
+  being. The flag is also available in `loop quote in` as an extension.
+* `--route_hints` has also been added on the `loop in` and `loop quote in` cli
+  commands, and was also include in [#415](https://github.com/lightninglabs/loop/pull/415).
+  While the `--private` flag autogenerates routehints to assist the payer (Lightning Labs),
+  `--route_hints` allows the user to feed their own crafted versions if they so please.
+
 #### Breaking Changes
 
 #### Bug Fixes