doc/protocols: move option follow entry to correct section

The entry for file protocol option 'follow' was inserted under ftp options
during merge of a Libav commit - 90eb2499. Corrected.

doc/protocols.texi

@@ -193,6 +193,12 @@ Set I/O operation maximum block size, in bytes. Default value is
 @code{INT_MAX}, which results in not limiting the requested block size.
 Setting this value reasonably low improves user termination request reaction
 time, which is valuable for files on slow medium.
+
+@item follow
+If set to 1, the protocol will retry reading at the end of the file, allowing
+reading files that still are being written. In order for this to terminate,
+you either need to use the rw_timeout option, or use the interrupt callback
+(for API users).
 @end table
 
 @section ftp
@@ -229,17 +235,6 @@ it, unless special care is taken (tests, customized server configuration
 etc.). Different FTP servers behave in different way during seek
 operation. ff* tools may produce incomplete content due to server limitations.
 
-This protocol accepts the following options:
-
-@table @option
-@item follow
-If set to 1, the protocol will retry reading at the end of the file, allowing
-reading files that still are being written. In order for this to terminate,
-you either need to use the rw_timeout option, or use the interrupt callback
-(for API users).
-
-@end table
-
 @section gopher
 
 Gopher protocol.