[DOCS] Actionable message for file lock errors (#634)

* [DOCS] Actionable message for file lock errors"

* pylint

src/ytdl_sub/utils/file_lock.py

@@ -44,7 +44,19 @@ else:
             / str(working_directory_path).replace("/", "_")
         )
 
-        lock_file = open(lock_file_path, "w", encoding="utf-8")
+        try:
+            lock_file = open(lock_file_path, "w", encoding="utf-8")
+        except FileNotFoundError as exc:
+            # pylint: disable=line-too-long
+            raise ValidationException(
+                "Failed to create a file-lock to prevent multiple instances of ytdl-sub from "
+                "colliding with each other. If you get this error, it typically means it tried to "
+                "create the file in a directory that is not a part of the same filesystem that "
+                "ytdl-sub is running on. See "
+                "https://ytdl-sub.readthedocs.io/en/latest/config.html#ytdl_sub.config.config_validator.ConfigOptions.lock_directory "
+                "on how to change the directory that this lock gets written to."
+            ) from exc
+            # pylint: enable=line-too-long
 
         try:
             fcntl.lockf(lock_file, fcntl.LOCK_EX | fcntl.LOCK_NB)