docs: Do not use relative URL to refer to integrations category.

We are changing individual integration docs to live at
integrations/{integration_name} instead of
integrations/doc/{integration_name}. Our relative link of
`../version-control` in this case will lead to `/version-control` on
the root of the web app instead of intended
`/integrations/version-control`.

We are also changing categories to live at
/integrations/category/{category_name` instead of
/integrations/{category_name} on the web app. But the web app will be
setting up redirects for existing categories to lead them to the new
URL. This commit specifies the /integrations/{category_name} temporarily
so that this PR can be merged before the changes in the web app and we
don't have worry about syncing the releases between the web app and
python-zulip-api.

Once the webapp code is merged, we should change all the relevant links
in this repo to use the new URL structure.

Author: shubham-padia

zulip/integrations/git/doc.md

@@ -51,4 +51,4 @@ In `{{ config_file_path }}`, you can set:
 - The message format used in your Zulip notifications by updating the
   `format_commit_message` function.
 
-[other-integrations]: ../version-control
+[other-integrations]: /integrations/version-control