trace doc: convert trace/kprobetrace.txt to rst format

This converts the plain text documentation to reStructuredText format and
add it into Sphinx TOC tree. No essential content change.

Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Changbin Du <changbin.du@intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/Documentation/trace/index.rst b/Documentation/trace/index.rst
index 947c6db..c8e2130 100644
--- a/Documentation/trace/index.rst
+++ b/Documentation/trace/index.rst
@@ -9,3 +9,4 @@
    tracepoint-analysis
    ftrace
    ftrace-uses
+   kprobetrace