add c# to code navigation (#16048)

Author: jf205

content/github/managing-files-in-a-repository/navigating-code-on-github.md

@@ -10,6 +10,7 @@ versions:
 ### About navigating code on {% data variables.product.prodname_dotcom %}
 
 Navigating code functions use the open source library [`semantic`](https://github.com/github/semantic). The following languages are supported:
+- C#
 - CodeQL
 - Go
 - Java