Make "Get Pages failed" error message more helpful

src/api-client.js

@@ -42,7 +42,11 @@ async function findOrCreatePagesSite({ githubToken, enablement = true }) {
     pageObject = await getPagesSite({ githubToken })
   } catch (error) {
     if (!enablement) {
-      core.error('Get Pages site failed', error)
+      core.error(
+        'Get Pages site failed. Make sure a version of your website is already deployed'
+        + 'on GitHub Pages, or consider setting `enablemet: true` for this action',
+        error
+      )
       throw error
     }
     core.warning('Get Pages site failed', error)