add title tag to head

This shows "$PAGE_TITLE | The Mesa 3D Graphics Library" in the title
field.

Closes: #4
4 jobs for master in 20 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #3409013
pages

00:00:20

 
  Deploy
passed pages:deploy

00:00:02

failed pages:deploy

00:00:00

failed pages:deploy

00:00:00