perf tools: Ignore Documentation dependency file

When building directly on the checked out repository the build process
produces a file that should be ignored, so add it to .gitignore.

Fixes: a81df63 ("perf doc: Fix doc.dep")
Reported-by: Linus Torvalds <[email protected]>
Signed-off-by: Ian Rogers <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lore.kernel.org/lkml/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

tools/perf/.gitignore

@@ -39,3 +39,4 @@ pmu-events/jevents
 feature/
 fixdep
 libtraceevent-dynamic-list
+Documentation/doc.dep