Update permissions for Linux (#9040)

Co-authored-by: Martin Dechev <dechevmartin@gmail.com>

Author: Wires77

.gitattributes

@@ -61,3 +61,9 @@
 #*.PDF   diff=astextplain
 #*.rtf   diff=astextplain
 #*.RTF   diff=astextplain
+
+###############################################################################
+# Executable files - preserve execution permissions on Unix systems
+# (https://git-scm.com/docs/gitattributes#_executable)
+###############################################################################
+runtime/*.exe binary

CONTRIBUTING.md

@@ -67,7 +67,7 @@ The easiest way to make and test changes is by setting up a development installa
        cd PathOfBuilding
 
 3. Start Path of Building from the repository by running `./runtime/Path{space}of{space}Building.exe`.
-
+   * <ins>Note for Linux users:</ins> The executable files should automatically have the correct permissions when cloned fresh. If you still encounter permission issues, run once: `chmod +x ./runtime/Path{space}of{space}Building-PoE2.exe`
 You can now use the shortcut to run the program from the repository. Running the program in this manner automatically enables "Dev Mode", which has some handy debugging feature:
 * `F5` restarts the program in-place (this is what usually happens when an update is applied).
 * `Ctrl` + `~` toggles the console (Note that this does not work with all keyboard layouts. US layout is a safe bet though).