document xsd support for pom and settings in guides

Your favorite IDE probably supports xsd schema's for pom.xml and settings.xml editing.
Yet very few have the defined the xsd in those files because they don't know about it.

The guides should note that pom.xml files best start with:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">

Why isn't it http://maven.apache.org/xsd/maven-v4_0_0.xsd (notice the xsd subdirectory) btw?

and the settings.xml starts with:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/???/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/???/4.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">

Of course, replace the ??? with something (I did "settings" but I ahve no idea if that's ok).