docs, kprobes: Remove invalid URL and add new reference

The following reference is invalid, remove it.
https://www.ibm.com/developerworks/library/l-kprobes/index.html

Add the following new reference "An introduction to KProbes":
https://lwn.net/Articles/132196/

Link: https://lkml.kernel.org/r/1635213091-24387-3-git-send-email-yangtiezhu@loongson.cnSigned-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

Documentation/trace/kprobes.rst

@@ -784,6 +784,6 @@ References
 
 For additional information on Kprobes, refer to the following URLs:
 
-- https://www.ibm.com/developerworks/library/l-kprobes/index.html
+- https://lwn.net/Articles/132196/
 - https://www.kernel.org/doc/ols/2006/ols2006v2-pages-109-124.pdf