Documentation: update .gitignore files

Add some missing files to .gitignore.
Push Documentation/.gitignore down into subdirectories.

Signed-off-by: Peter Foley <pefoley2@pefoley.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/Documentation/prctl/.gitignore b/Documentation/prctl/.gitignore
new file mode 100644
index 0000000..0b5c274
--- /dev/null
+++ b/Documentation/prctl/.gitignore
@@ -0,0 +1,3 @@
+disable-tsc-ctxt-sw-stress-test
+disable-tsc-on-off-stress-test
+disable-tsc-test