manual: add download-infra.txt

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

docs/manual/developer-guide.txt

@@ -7,4 +7,6 @@ include::writing-rules.txt[]
 
 include::adding-packages.txt[]
 
+include::download-infra.txt[]
+
 include::board-support.txt[]

docs/manual/download-infra.txt

@@ -0,0 +1,8 @@
+// -*- mode:doc -*- ;
+
+[[download-infra]]
+
+Download infrastructure
+-----------------------
+
+TODO

docs/manual/prerequisite.txt

@@ -61,7 +61,7 @@ using +wget+, few are only available through their +git+, +mercurial+,
 or +svn+ repository.
 +
 All other source fetching methods are implemented and may be used in a
-development context.
+development context (further details: refer to xref:download-infra[]).
 +
 ** +bazaar+
 ** +cvs+