Make the list of main branches configurable

src/hike/data/config.py

@@ -34,6 +34,9 @@ class Configuration:
     command_line_on_top: bool = False
     """Should the command line live at the top of the screen?"""
 
+    main_branches: list[str] = field(default_factory=lambda: ["main", "master"])
+    """The branches considered to be main branches on forges."""
+
 
 ##############################################################################
 def configuration_file() -> Path:

src/hike/messages/opening.py

@@ -16,6 +16,7 @@
 ##############################################################################
 # Local imports.
 from .. import USER_AGENT
+from ..data import load_configuration
 from ..types import HikeLocation
 
 
@@ -78,7 +79,7 @@ async def url(self) -> URL | None:
         filename = self.filename or "README.md"
         async with AsyncClient() as client:
             for candidate_branch in (
-                (self.branch,) if self.branch else ("main", "master")
+                [self.branch] if self.branch else load_configuration().main_branches
             ):
                 url = self.raw_url_format.format(
                     owner=self.owner,