DOCS/man/options: document @ syntax for --input-ipc-server

DOCS/man/options.rst

@@ -4487,8 +4487,11 @@ Input
 ``--input-ipc-server=<filename>``
     Enable the IPC support and create the listening socket at the given path.
 
-    On Linux and Unix, the given path is a regular filesystem path. On Windows,
-    named pipes are used, so the path refers to the pipe namespace
+    On Linux and Unix, if the first character of the path is ``@``, then it
+    is internally replaced with a null character, which represents an abstract
+    socket address on Linux, but can have unspecified behavior on other UNIX
+    platforms. Otherwise, the given path is a regular filesystem path.
+    On Windows, named pipes are used, so the path refers to the pipe namespace
     (``\\.\pipe\<name>``). If the ``\\.\pipe\`` prefix is missing, mpv will add
     it automatically before creating the pipe, so
     ``--input-ipc-server=/tmp/mpv-socket`` and