vscode: add docs about goto-definition for rust syntax tree

Author: Veetaha

docs/user/features.md

@@ -85,6 +85,10 @@ You can hover over syntax nodes in the opened text file to see the appropriate
 rust code that it refers to and the rust editor will also highlight the proper
 text range.
 
+If you press <kbd>Ctrl</kbd> (i.e. trigger goto definition) in the inspected
+Rust source file the syntax tree readonly editor should scroll to and select the
+appropriate syntax node token.
+
 <img src="https://user-images.githubusercontent.com/36276403/78043783-7425e180-737c-11ea-8653-b02b773c5aa1.png" alt="demo" height="200px" >
 
 #### Expand Macro Recursively