Add AppImage path discovery

Signed-off-by: Loren Eteval <loren.eteval@proton.me>

Furious/Utility/SystemRuntime.py

@@ -30,6 +30,7 @@ import subprocess
 __all__ = [
     'getPythonVersion',
     'getUbuntuRelease',
+    'getAppImagePath',
     'isAdministrator',
     'isTUNMode',
     'isScriptMode',
@@ -71,6 +72,16 @@ def getUbuntuRelease() -> str:
         return ''
 
 
+def getAppImagePath() -> str:
+    if PLATFORM != 'Linux':
+        return ''
+
+    if 'APPIMAGE' in os.environ:
+        return os.environ['APPIMAGE']
+    else:
+        return ''
+
+
 @functools.lru_cache(None)
 def isAdministrator() -> bool:
     if PLATFORM == 'Windows':