Fix link in the docs changes issue template

Author: DarthSim

.github/templates/ISSUE.md

@@ -3,5 +3,5 @@ title: Usage docs of imgproxy have been updated
 assignees: DarthSim
 labels: enhancement
 ---
-@{{ payload.client_payload.actor }} has just updated the [Usage](https://docs.imgproxy.net/usage) part of the documentation.
+@{{ payload.client_payload.actor }} has just updated the [Usage](https://docs.imgproxy.net/category/usage) part of the documentation.
 Please, check [the difference]({{ payload.client_payload.link }}) and make the necessary changes.