Fix documenting-arguments anchor in docs

Judging from other places in the documentation which link to this
anchor, this anchor is misplaced.

Author: meator

docs/documentation.rst

@@ -30,8 +30,6 @@ Simple example:
     invoke(hello, args=['--help'])
 
 
-.. _documenting-arguments:
-
 Command Short Help
 ------------------
 
@@ -70,6 +68,8 @@ The help epilog is printed at the end of the help and is useful for showing exam
 
     invoke(init, args=['--help'])
 
+.. _documenting-arguments:
+
 Documenting Arguments
 ----------------------