getting started: fix non-referencable page anchor

the default highlighting directive put between page anchor got in the way of
extracting page title, making the page non-referencable

docs/getting-started.rst

 .. _getting-started:
 
-.. highlight:: bash
-
-
 Run your own Software Heritage
 ==============================
 
@@ -13,6 +10,8 @@ steps detailed below:
 
 .. contents:: :local:
 
+.. highlight:: bash
+
 
 Step 0 --- get the code
 -----------------------