Improve error message when get_pages_url fails

CHANGELOG.md

@@ -9,6 +9,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/)
 ### Changed
 
 * Print stdout and stderr when shell commands fail (fixes [#63](https://github.com/hexdoc-dev/hexdoc/issues/63)).
+* Improve the error message when GitHub Pages is not enabled.
 
 ## `1!0.1.0a12`
 

src/hexdoc/cli/ci.py

@@ -11,7 +11,7 @@
 from pathlib import Path
 from typing import Literal, TypedDict, TypeVar, Unpack
 
-from github import Auth, Github
+from github import Auth, Github, UnknownObjectException
 from github.Repository import Repository
 from pydantic import TypeAdapter
 from typer import Typer
@@ -149,6 +149,11 @@ def get_pages_url(repo: Repository) -> str:
         _, data = repo._requester.requestJsonAndCheck("GET", endpoint)
     except Exception as e:
         e.add_note(f"  Endpoint: {endpoint}")
+        if isinstance(e, UnknownObjectException):
+            e.add_note(
+                "Note: check if GitHub Pages is enabled in this repo"
+                + " (https://github.com/hexdoc-dev/hexdoc-hexcasting-template/blob/d6f918f6f115/README.md#setting-up-pages)"
+            )
         raise
     return str(data["html_url"])