Fix JetBrains Rider arguments in Using an external text editor (#6019)

Adding the project folder to the exec args lets Rider open the project's folder
as a project and still also open the specified file.

This resolves an issue where if I open a file in a folder from Godot, the folder is treated
by Rider incorrectly as the project root.

tutorials/editor/external_editor.rst

@@ -37,7 +37,7 @@ Some example Exec Flags for various editors include:
 +---------------------+-----------------------------------------------------+
 | Atom/Sublime Text   | ``{file}:{line}``                                   |
 +---------------------+-----------------------------------------------------+
-| JetBrains Rider     | ``--line {line} {file}``                            |
+| JetBrains Rider     | ``{project} --line {line} {file}``                  |
 +---------------------+-----------------------------------------------------+
 | Visual Studio Code  | ``{project} --goto {file}:{line}:{col}``            |
 +---------------------+-----------------------------------------------------+