doc: use @code{} for --{enable,disable}-options.

doc/filters.texi

@@ -93,7 +93,7 @@ Follows a BNF description for the filtergraph syntax:
 @c man begin AUDIO FILTERS
 
 When you configure your FFmpeg build, you can disable any of the
-existing filters using --disable-filters.
+existing filters using @code{--disable-filters}.
 The configure output will show the audio filters included in your
 build.
 
@@ -653,7 +653,7 @@ tools.
 @c man begin VIDEO FILTERS
 
 When you configure your FFmpeg build, you can disable any of the
-existing filters using --disable-filters.
+existing filters using @code{--disable-filters}.
 The configure output will show the video filters included in your
 build.
 
@@ -1413,7 +1413,7 @@ format=yuv420p:yuv444p:yuv410p
 Apply a frei0r effect to the input video.
 
 To enable compilation of this filter you need to install the frei0r
-header and configure FFmpeg with --enable-frei0r.
+header and configure FFmpeg with @code{--enable-frei0r}.
 
 The filter supports the syntax:
 @example
@@ -1772,7 +1772,7 @@ Pass the video source unchanged to the output.
 Apply video transform using libopencv.
 
 To enable this filter install libopencv library and headers and
-configure FFmpeg with --enable-libopencv.
+configure FFmpeg with @code{--enable-libopencv}.
 
 The filter takes the parameters: @var{filter_name}@{:=@}@var{filter_params}.
 
@@ -3017,7 +3017,7 @@ will generate a "dc_luma" test pattern.
 Provide a frei0r source.
 
 To enable compilation of this filter you need to install the frei0r
-header and configure FFmpeg with --enable-frei0r.
+header and configure FFmpeg with @code{--enable-frei0r}.
 
 The source supports the syntax:
 @example