docs: Add missing colon to README (#33)

README.md

@@ -212,7 +212,7 @@ def http_requested_languages_total() -> Callable[[Info], None]:
     def instrumentation(info: Info) -> None:
         langs = set()
         lang_str = info.request.headers["Accept-Language"]
-        for element in lang_str.split(",")
+        for element in lang_str.split(","):
             element = element.split(";")[0].strip().lower()
             langs.add(element)
         for language in langs: