docs: Document feature

README.md

@@ -17,6 +17,7 @@ Functionality:
 - Highlights the first syntax errors ProVerif finds with the corresponding error. For libraries, see below.
 - Press `CTRL` and click on an identifier to navigate to its definition or find all references of the definition.
 - Press `F2` to rename an identifier.
+- Press `CTRL`+`SHIFT`+`Space` to show signature help (automatically shown when typing `(`)
 - Press `CTRL`+`SHIFT`+`B` to execute ProVerif over the currently opened file.
 - Configure the proverif bin in the settings, else it is taken from the `$PATH`.