Update permissions for Linux (PathOfBuildingCommunity#1171)

* Add execute permissions to current 'exe' files

* Preserve execution permissions for executable files on Unix systems

* Update CONTRIBUTING.md with permissions info for Linux

Author: TheDechev

.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

@@ -68,6 +68,8 @@ The easiest way to make and test changes is by setting up a development installa
 
 3. Start Path of Building from the repository by running `./runtime/Path{space}of{space}Building-PoE2.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).