doc/encoders: apply various fixes to libmp3lame documentation

doc/encoders.texi

@@ -428,16 +428,16 @@ the LAME-equivalent options follow the FFmpeg ones.
 @multitable @columnfractions .2 .2
 @item FFmpeg            @tab LAME
 @item b                 @tab b
-FFmpeg @code{b} option is expressed in bits/s, lame @code{bitrate}
-in kilobits/s.
+Set bitrate expressed in bits/s, LAME @code{bitrate} is expressed in
+kilobits/s.
 @item q                 @tab V
-Quality setting for VBR.
+Set quality setting for VBR.
 @item compression_level @tab q
-Algorithm quality. Valid options are integers from 0-9.
+Set algorithm quality. Valid arguments are integers in the 0-9 range.
 @item reservoir         @tab N.A.
 Enable use of bit reservoir. LAME has this enabled by default.
 @item joint_stereo      @tab -m j
-Enables the encoder to use (on a frame by frame basis) either L/R
+Enable the encoder to use (on a frame by frame basis) either L/R
 stereo or mid/side stereo.
 @end multitable