doc/ffserver: fix typos/reword paragraphs about FFM versions

doc/ffserver.texi

@@ -240,13 +240,13 @@ For example:   @samp{http://localhost:8080/test.asf?date=2002-07-26T23:05:00}.
 
 @section What is FFM, FFM2
 
-FFM and FFM2 are formats used by ffserver, they allow storing a wide varity of
-video and audio streams, encoding options and can store a moving time segment
-of a infinite movie or a whole movie.
+FFM and FFM2 are formats used by ffserver. They allow storing a wide varity of
+video and audio streams and encoding options, and can store a moving time segment
+of an infinite movie or a whole movie.
 
-FFM, is version specific, there is limited compatibility of FFM files
+FFM is version specific, and there is limited compatibility of FFM files
 generated by one version of ffmpeg/ffserver and another version of
-ffmpeg/ffserver. It may work but its not guranteed to work.
+ffmpeg/ffserver. It may work but its not guaranteed to work.
 
 FFM2 is extensible while maintaining compatibility and should work between
 differing versions of tools. FFM2 is the default.