Fix link in troubleshooting docs
The linked issue is not rendered in Read the docs as a link.
This change fixes the rendering to follow the `[fluxcd/flux#number]` format used
else where in the docs.
@@ -9,7 +9,7 @@ explain workarounds.
If you notice that Flux takes tens of seconds or minutes to get
through each sync, while you can apply the same manifests very quickly
by hand, you may be running into this issue:
-https://github.com/fluxcd/flux/issues/1422
+[fluxcd/flux#1422](https://github.com/fluxcd/flux/issues/1422).
Briefly, the problem is that mounting a volume into `$HOME/.kube`
effectively disables `kubectl`'s caching, which makes it much much
