docs: changelog: add mention of gateway file to v0.15

docs/changelogs/v0.15.md

@@ -12,6 +12,7 @@ Below is an outline of all that is in this release, so you get a sense of all th
     - [🔦 Highlights](#-highlights)
       - [#️⃣ Blake 3 support](#️⃣-blake-3-support)
       - [💉 Fx Options plugin](#-fx-options-plugin)
+      - [📁 `$IPFS_PATH/gateway` file](#-ipfs_pathgateway-file)
     - [Changelog](#changelog)
     - [Contributors](#contributors)
 
@@ -51,6 +52,17 @@ func (p *PinnerPlugin) Options(info core.FXNodeInfo) ([]fx.Option, error) {
 
 Extra plugin info [here](https://github.com/ipfs/kubo/blob/master/docs/plugins.md#fx-experimental).
 
+#### 📁 `$IPFS_PATH/gateway` file
+
+This adds a new file in the `IPFS_PATH` folder similar to `$IPFS_PATH/api` containing an address based on [`Addresses.Gateway`](https://github.com/ipfs/kubo/blob/master/docs/config.md#addressesgateway) configuration.
+
+This file is in URL (RFC1738) format.
+
+```console
+$ cat ~/.ipfs/gateway
+http://127.0.0.1:8080
+```
+
 ### Changelog
 
 <details>