docs: note on extending the duration of a site (#147)

Signed-off-by: giac-mysten <[email protected]>

docs/walrus-sites/builder-config.md

@@ -10,9 +10,9 @@ here the details for all the configuration options.
 
 ## Minimal configuration
 
-The config file is expected to be in `./builder.yaml`, and it is possible to point elsewhere with
-the `--config` flag. For your first run, it should be sufficient to call the `site-builder` with
-`--config site-builder/assets/builder-example.yaml`, which is already configured appropriately.
+The config file is expected to be in `./sites-config.yaml`, and it is possible to point elsewhere
+with the `--config` flag. For your first run, it should be sufficient to call the `site-builder`
+with `--config sites-config.yaml`, which is already configured appropriately.
 
 If, for any reason, you didn't add `walrus` to `$PATH`, make sure to configure a pointer to the
 binary, see below.

docs/walrus-sites/tutorial-publish.md

@@ -96,3 +96,9 @@ Browsing to the provided URL should reflect the change. You've updated the site!
 ```admonish note
 The wallet you are using must be the *owner* of the Walrus Site object to be able to update it.
 ```
+
+```admonish danger title="Extending the expiration date of an existing site"
+To extend the expiration date of a previously-stored site, use the `update` command with the
+`--force` flag, and specify the number of additional epochs (from the current epoch) with the
+`--epochs` flag.
+```