doc workflow: generate source links to main revision

.github/workflows/docs.yml

@@ -44,7 +44,7 @@ jobs:
             (ql:quickload :coalton/doc)
             (uiop:symbol-call :coalton/doc :write-stdlib-documentation-to-file
               "/__w/coalton/coalton/coalton-website/content/reference.md" 
-              :backend :hugo))
+              :backend :hugo :revision "main"))
           EOF
           sbcl --noinform --non-interactive --load run-docs.lisp --eval "(main)"