xbps: elaborate on building packages, move to bottom

this is not something that should be the first thing in the list of
subsections about "how to use xbps", so move it down. Incorporates
suggestions from #639.

closes: #639
closes: #847

Author: classabbyamp

src/xbps/index.md

@@ -30,10 +30,6 @@ Most general package management is done with the following commands:
 Most questions can be answered by consulting the man pages for these tools,
 together with the [xbps.d(5)](https://man.voidlinux.org/xbps.d.5) man page.
 
-To learn how to build packages from source, refer to [the README for the
-void-packages
-repository](https://github.com/void-linux/void-packages/blob/master/README.md).
-
 ## Updating
 
 Like any other system, it is important to keep Void up-to-date. Use
@@ -125,3 +121,13 @@ To get a list of all installed packages, without their version:
 ```
 $ xbps-query -l | awk '{ print $2 }' | xargs -n1 xbps-uhelper getpkgname
 ```
+
+## Building Packages
+
+To learn how to build packages from source, refer to the [void-packages
+repository](https://github.com/void-linux/void-packages). In that repository,
+the [README](https://github.com/void-linux/void-packages/blob/master/README.md)
+provides a general overview of the `xbps-src` tool and instructions for building
+packages locally from existing package templates. For information about how to
+add new templates or modify existing ones, refer to the
+[Manual](https://github.com/void-linux/void-packages/blob/master/Manual.md).