docs: trace: fix some Sphinx warnings

There are some warnings produced when building trace. Fix them.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/trace/ftrace.rst

@@ -1404,6 +1404,7 @@ trace has provided some very helpful debugging information.
 
 If we prefer function graph output instead of function, we can set
 display-graph option::
+
  with echo 1 > options/display-graph
 
   # tracer: irqsoff

Documentation/trace/histogram.rst

@@ -2133,7 +2133,7 @@ The following commonly-used handler.action pairs are available:
     the end the event that triggered the snapshot (in this case you
     can verify the timestamps between the sched_waking and
     sched_switch events, which should match the time displayed in the
-    global maximum):
+    global maximum)::
 
      # cat /sys/kernel/debug/tracing/snapshot
 
@@ -2213,9 +2213,10 @@ The following commonly-used handler.action pairs are available:
     following the rest of the fields.
 
     If a snaphot was taken, there is also a message indicating that,
-    along with the value and event that triggered the snapshot:
+    along with the value and event that triggered the snapshot::
 
       # cat /sys/kernel/debug/tracing/events/tcp/tcp_probe/hist
+
       { dport:       1521 } hitcount:          8
 	changed:         10  snd_wnd:      35456  srtt:     154262  rcv_wnd:      42112
 
@@ -2228,7 +2229,8 @@ The following commonly-used handler.action pairs are available:
       { dport:        443 } hitcount:        211
 	changed:         10  snd_wnd:      26960  srtt:      17379  rcv_wnd:      28800
 
-    Snapshot taken (see tracing/snapshot).  Details:
+    Snapshot taken (see tracing/snapshot).  Details::
+
         triggering value { onchange($cwnd) }:         10
         triggered by event with key: { dport:         80 }
 
@@ -2245,7 +2247,7 @@ The following commonly-used handler.action pairs are available:
     the global snapshot).
 
     And finally, looking at the snapshot data should show at or near
-    the end the event that triggered the snapshot:
+    the end the event that triggered the snapshot::
 
       # cat /sys/kernel/debug/tracing/snapshot