How to make favicons using NetPBM

Creating a favicon for a site using the highly recommended NetPBM:

ppmtowinicon -o favicon.ico \
    <( pngtopnm favicon-16x16.png | ppmquant 15 ) \
    <( pngtopnm favicon-32x32.png | ppmquant 15 )

Adding it to a page:

<link rel="icon" href="/favicon.ico" type="image/x-icon" />
<link rel="shortcut icon" href="/favicon.ico" type="image/x-icon" />