Fix redirect link on Tuning.md (#1595)

docs/Running-Mastodon/Tuning.md

@@ -1 +1 @@
-[The documentation has moved to its own repository](https://github.com/tootsuite/documentation/blob/master/Running-Mastodon/Tuning-guide.md)
+[The documentation has moved to its own repository](https://github.com/tootsuite/documentation/blob/master/Running-Mastodon/Tuning.md)