[doc] Don't use non-ASCII quotes in code

Signed-off-by: Philipp Wagner <phw@lowrisc.org>
diff --git a/doc/ug/github_notes.md b/doc/ug/github_notes.md
index ffb5d01..04ca7e5 100644
--- a/doc/ug/github_notes.md
+++ b/doc/ug/github_notes.md
@@ -453,7 +453,7 @@
 
     ```console
     $ git add...
-    $ git commit -m “Add CFG examples to UART specification”
+    $ git commit -m "Add CFG examples to UART specification"
     ```
 
 * Step 3: Create your github branch for the pull request