notify the user about serial access

REVHubInterface/__main__.py

@@ -9,12 +9,15 @@
 import os
 import datetime
 import traceback
-
+import REVHubInterface.serialaccess as serialaccess
 # try:
 #     import ft232
 # except Exception as e: 
 #     print(platform.system)
 #     tkinter.messagebox.showerror('Drivers Not Detected', 'Please verify the correct drivers are installed.  Without the correct dirvers, firmware update functionality will be unavailable.\n\n - Windows 10 and above should automatically install the correct drivers when the Expansion Hub is plugged in.\n\n - Windows 7 requires a manual install. Please see this link for the correct driver (FTDI D2xx): https://www.ftdichip.com/Drivers/CDM/CDM21228_Setup.zip\n\n - On macOS, install libftdi via Homebrew: "brew install libftdi"\n\n - On Linux, install libftdi.  On Debian/Ubuntu-based systems, install it via "sudo apt install libftdi1"\n\nException Message:\n' + str(e))
+if not serialaccess.hasAccess(): 
+    tkinter.messagebox.showerror("User does not have serial access", "Your user does not have access to serial. Switch to a user that does, or add your user to a group that has serial access.\nhttps://github.com/unofficial-rev-port/REVHubInterface/blob/main/README.md#access-to-serial-on-linux")
+
 def error(windowName: str, error: Exception) -> None:
     errName = str(error)
     print(errName)

REVHubInterface/serialaccess.py

@@ -0,0 +1,12 @@
+import grp
+import os, sys
+
+def hasAccess():
+    if sys.platform == "linux":
+        try:
+            groups = [g.gr_name for g in grp.getgrall() if os.getlogin() in g.gr_mem]
+            if 'dialout' in groups or 'uucp' in groups: return True
+            return False
+        except KeyError:
+            return False
+    else: return True