DOCS: fix description of subtitle delay adjustment

Modified the man page.

There were two pairs of key bindings that appeared in one order but
the description of what they do appeared in the reverse order. Modified
the description to match the order in which the keys appear.

Note: I have not tested this change.

DOCS/man/mpv.rst

@@ -66,7 +66,7 @@ Ctrl+LEFT and Ctrl+RIGHT
     might not always work; see ``sub-seek`` command.
 
 Ctrl+Shift+LEFT and Ctrl+Shift+RIGHT
-    Adjust subtitle delay so that the next or previous subtitle is displayed
+    Adjust subtitle delay so that the previous or next subtitle is displayed
     now. This is especially useful to sync subtitles to audio.
 
 [ and ]
@@ -161,7 +161,7 @@ j and J
     Cycle through the available subtitles.
 
 z and Z
-    Adjust subtitle delay by +/- 0.1 seconds. The ``x`` key does the same as
+    Adjust subtitle delay by -/+ 0.1 seconds. The ``x`` key does the same as
     ``Z`` currently, but use is discouraged.
 
 l