Add command to fix broken permissions to Linux installation instructions (#1148)

Co-authored-by: Oleksii Holub <1935960+Tyrrrz@users.noreply.github.com>

.docs/Linux.md

@@ -15,6 +15,10 @@ Please follow the [instructions provided here](https://github.com/Tyrrrz/Discord
 dotnet DiscordChatExporter.Cli.dll export -t TOKEN -c CHANNEL
 ```
 
+If the above command throws a "Permission denied" error, execute this command to fix the permissions:
+
+```console
+chmod 644 *.dll DiscordChatExporter.*
 > [How to get Token and Channel IDs](https://github.com/Tyrrrz/DiscordChatExporter/blob/master/.docs/Token-and-IDs.md).
 
 There's much more you can do with DCE.CLI! Read the [CLI explained](https://github.com/Tyrrrz/DiscordChatExporter/blob/master/.docs/Getting-started.md#dcecli-commands-) page to get started.