perf dlfilter: Amend documentation wrt library dependencies

Like all locally-built programs, dlfilters may need to be re-built if
shared libraries they use change. Also there may be unexpected results
if the dfilter uses different versions of the shared libraries that perf
uses.

Note those things in the documentation.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: https //lore.kernel.org/r/20210811101036.17986-5-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-dlfilter.txt

@@ -246,6 +246,14 @@ To use the filter with perf script:
 
 	perf script --dlfilter dlfilter-example.so
 
+NOTES
+-----
+
+The dlfilter .so file will be dependent on shared libraries. If those change,
+it may be necessary to rebuild the .so. Also there may be unexpected results
+if the .so uses different versions of the shared libraries that perf uses.
+Versions can be checked using the ldd command.
+
 SEE ALSO
 --------
 linkperf:perf-script[1]