triagebot: Enable the range-diff feature

Author: tgross35

triagebot.toml

@@ -19,3 +19,8 @@ check-commits = false
 # Enable issue transfers within the org
 # Documentation at: https://forge.rust-lang.org/triagebot/transfer.html
 [transfer]
+
+# Enable comments linking to triagebot range-diff when a PR is rebased
+# onto a different base commit
+# Documentation at: https://forge.rust-lang.org/triagebot/range-diff.html
+[range-diff]