docs/manual: fix cross-reference

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

docs/manual/adding-packages.txt

@@ -1,5 +1,6 @@
 Adding new packages to Buildroot
 ================================
+[[adding-packages]]
 
 This section covers how new packages (userspace libraries or
 applications) can be integrated into Buildroot. It also shows how

docs/manual/rebuilding-packages.txt

@@ -29,7 +29,7 @@ by the different packages, so some understanding of the particular
 package is needed.
 
 For packages relying on Buildroot packages infrastructures (see
-xref:add-packages[this section] for details), the following stamp
+xref:adding-packages[this section] for details), the following stamp
 files are relevant:
 
 * +output/build/packagename-version/.stamp_configured+. If removed,