Add FAQ item about coreboot

As touched on in IRC with holger and marek. New and existing users are often confused about what hardware to buy and whether coreboot is superior to vendor bios.  I've tried to keep this entry concise (it could already be considering too long) what I've tried to do is include the most often asked questions without writing a tutorial which is probably out of scope for the Qubes website and better left to the coreboot wiki. I've ignored libreboot here as it is not part of the certified hardware requirements and I don't recall a report of success.

about/faq.md

@@ -115,6 +115,10 @@ At the same time, due to the smart use of Xen shared memory, our GUI implementat
 
 Please refer to [this page](/doc/vm-sudo/).
 
+### Do you recommend coreboot as an alternative to vendor BIOS?
+
+Yes, where it is possible to use it an open source boot firmware ought to be more trustable than a closed source implementation.   [coreboot](https://www.coreboot.org/) is as a result a requirement for [Qubes Certified Hardware](https://www.qubes-os.org/news/2016/07/21/new-hw-certification-for-q4/). The number of machines coreboot currently supports is limited and the use of some vendor supplied blobs is generally still required. Where coreboot does support your machine and is not already installed, you will generally need additional hardware to flash it. Please see the coreboot website / their IRC channel for further information.
+
 ### How should I report documentation issues?
 
 Please see the [documentation guidelines](/doc/doc-guidelines).