docs(logs): Mimick argparse option default format

I find it more readable to use punctuation to separate technical information, such as
required vs optional or default values, from narrative description. Follow argparse's
lead, and put such information in parens following the narrative description.

src/ytdl_sub/config/config_validator.py

@@ -67,7 +67,7 @@ class PersistLogsValidator(StrictDictValidator):
     @property
     def logs_directory(self) -> str:
         """
-        Required. The directory to store the logs in.
+        The directory to store the logs in. (required)
         """
         return self._logs_directory.value
 
@@ -92,7 +92,7 @@ class PersistLogsValidator(StrictDictValidator):
     @property
     def keep_successful_logs(self) -> bool:
         """
-        Optional. Whether to store logs when downloading is successful. Defaults to True.
+        Whether to store logs when downloading is successful. (default ``True``)
         """
         return self._keep_successful_logs.value
 
@@ -147,7 +147,7 @@ class ConfigOptions(StrictDictValidator):
     def working_directory(self) -> str:
         """
         The directory to temporarily store downloaded files before moving them into their final
-        directory. Defaults to .ytdl-sub-working-directory
+        directory. (default ``./.ytdl-sub-working-directory``)
         """
         # Expands tildas to actual paths, use native os sep
         return os.path.expanduser(self._working_directory.value.replace(posixpath.sep, os.sep))
@@ -155,7 +155,7 @@ class ConfigOptions(StrictDictValidator):
     @property
     def umask(self) -> Optional[str]:
         """
-        Umask (octal format) to apply to every created file. Defaults to "022".
+        Umask in octal format to apply to every created file. (default ``022``)
         """
         return self._umask.value
 
@@ -214,24 +214,25 @@ class ConfigOptions(StrictDictValidator):
     def lock_directory(self) -> str:
         """
         The directory to temporarily store file locks, which prevents multiple instances
-        of ``ytdl-sub`` from running. Note that file locks do not work on network-mounted
-        directories. Ensure that this directory resides on the host machine. Defaults to ``/tmp``.
+        of ``ytdl-sub`` from running. Note that file locks do not work on
+        network-mounted directories. Ensure that this directory resides on the host
+        machine. (default ``/tmp``)
         """
         return self._lock_directory.value
 
     @property
     def ffmpeg_path(self) -> str:
         """
-        Path to ffmpeg executable. Defaults to ``/usr/bin/ffmpeg`` for Linux, and
-        ``ffmpeg.exe`` for Windows (in the same directory as ytdl-sub).
+        Path to ffmpeg executable. (default ``/usr/bin/ffmpeg`` for Linux,
+        ``./ffmpeg.exe`` in the same directory as ytdl-sub for Windows)
         """
         return self._ffmpeg_path.value
 
     @property
     def ffprobe_path(self) -> str:
         """
-        Path to ffprobe executable. Defaults to ``/usr/bin/ffprobe`` for Linux, and
-        ``ffprobe.exe`` for Windows (in the same directory as ytdl-sub).
+        Path to ffprobe executable. (default ``/usr/bin/ffprobe`` for Linux,
+        ``./ffprobe.exe`` in the same directory as ytdl-sub for Windows)
         """
         return self._ffprobe_path.value