Docs: link to man pages for pipe and socketpair

[skip ci]

Author: aantron

src/TCP.mli

@@ -60,7 +60,9 @@ val socketpair :
 (** Creates a pair of connected sockets.
 
     Binds {{:http://docs.libuv.org/en/v1.x/tcp.html#c.uv_socketpair}
-    [uv_socketpair]}.
+    [uv_socketpair]}. See
+    {{:https://www.man7.org/linux/man-pages/man3/socketpair.3p.html}
+    [socketpair(3p)]}.
 
     See {!Luv.Pipe.pipe} for an explanation of the optional arguments.
 

src/pipe.mli

@@ -42,7 +42,8 @@ val pipe :
     (File.t * File.t, Error.t) result
 (** Creates a pair of connected pipes.
 
-    Binds {{:http://docs.libuv.org/en/v1.x/pipe.html#c.uv_pipe} [uv_pipe]}.
+    Binds {{:http://docs.libuv.org/en/v1.x/pipe.html#c.uv_pipe} [uv_pipe]}. See
+    {{:https://www.man7.org/linux/man-pages/man3/pipe.3p.html} [pipe(3p)]}.
 
     In case of success, in the value [(read_pipe, write_pipe)], data written
     to [write_pipe] can be read from [read_pipe].