docs: add troubleshooting section for macOS & Linux

Add a Troubleshooting section to the README covering two common
platform-specific launch issues and how to resolve them.

- macOS: document Gatekeeper "App is damaged and can't be opened"
  and show how to clear the quarantine flag with xattr.
- Linux: document chrome-sandbox SUID permission error and provide
  two solutions — fix permissions (chown/chmod) for packaged installs,
  or run with --no-sandbox by editing the desktop launcher or using the
  command line.

These instructions reduce user confusion and support requests by
providing clear, actionable steps to get IPTVnator running on affected
systems.

README.md

@@ -108,6 +108,63 @@ sudo emerge iptvnator-bin
 
 <a href="https://github.com/sponsors/4gray" target="_blank"><img src="https://cdn.buymeacoffee.com/buttons/default-green.png" alt="Buy Me A Coffee" width="185"></a>
 
+## Troubleshooting
+
+### macOS: "App is damaged and can't be opened"
+
+Due to Apple's Gatekeeper security and code signing requirements, you may need to remove the quarantine flag from the downloaded application:
+
+```bash
+xattr -c /Applications/IPTVnator.app
+```
+
+Alternatively, if the app is located in a different directory:
+
+```bash
+xattr -c ~/Downloads/IPTVnator.app
+```
+
+### Linux: chrome-sandbox Issues
+
+If you encounter the following error when launching IPTVnator:
+
+```
+The SUID sandbox helper binary was found, but is not configured correctly.
+Rather than run without sandboxing I'm aborting now.
+You need to make sure that chrome-sandbox is owned by root and has mode 4755.
+```
+
+**Solution 1: Fix chrome-sandbox permissions (Recommended for .deb/.rpm installations)**
+
+Navigate to the IPTVnator installation directory and run:
+
+```bash
+sudo chown root:root chrome-sandbox
+sudo chmod 4755 chrome-sandbox
+```
+
+**Solution 2: Launch with --no-sandbox flag**
+
+Edit the desktop launcher file to add the `--no-sandbox` flag:
+
+1. Find your desktop file location:
+   - **Ubuntu/Debian**: `~/.local/share/applications/iptvnator.desktop`
+   - **System-wide**: `/usr/share/applications/iptvnator.desktop`
+
+2. Edit the file and modify the `Exec` line:
+
+   ```
+   Exec=iptvnator --no-sandbox %U
+   ```
+
+3. Save the file and relaunch the application from your application menu.
+
+Alternatively, you can launch IPTVnator from the terminal with the flag:
+
+```bash
+iptvnator --no-sandbox
+```
+
 ## How to Build and Develop
 
 Requirements: