chore: add CHANGELOG entry

Author: route

CHANGELOG.md

@@ -9,6 +9,7 @@
 - `Ferrum::Network::Exchange#unknown` determines if the exchange is in an unknown state, meaning that browser might not return info about it [#426]
 - `Ferrum::Network::Exchange#loader_id` returns loader id [#426]
 - `Ferrum::Browser#debug` opens headless session in the browser devtools frontend [#519]
+- `Ferrum::Frame#parent` returns the parent frame if this frame is nested [#523]
 
 ### Changed
 

README.md

@@ -1084,6 +1084,10 @@ Frame's unique id.
 
 Parent frame id if this one is nested in another one.
 
+#### parent : `Frame | nil`
+
+Parent frame if this one is nested in another one.
+
 #### execution_id : `Integer`
 
 Execution context id which is used by JS, each frame has it's own context in