doc/filters: apply minor fixes

doc/filters.texi

@@ -5468,12 +5468,11 @@ previous output PTS
 previous output time in seconds
 
 @item RTCTIME
-wallclock (RTC) time in microseconds
-Deprecated, use time(0)
+wallclock (RTC) time in microseconds. This is deprecated, use time(0)
+instead.
 
 @item RTCSTART
 wallclock (RTC) time at the start of the movie in microseconds
-
 @end table
 
 @subsection Examples
@@ -5516,7 +5515,7 @@ setpts=PTS+10/TB
 @end example
 
 @item
-generate timestamps from a "live source" and rebase onto the current timebase
+Generate timestamps from a "live source" and rebase onto the current timebase:
 @example
 setpts='(RTCTIME - RTCSTART) / (TB * 1000000)'
 @end example