Link to QEMU build commands in the FAQ from the "Build an run" page

The quick QEMU build instructions are in the FAQ and are not linked from
the "Build and run" page. Therefore they are a bit difficult to find.
This commit adds a link.

Signed-off-by: Jerome Forissier <jerome@forissier.org>
Reviewed-by: Joakim Bech <joakim.bech@linaro.org>
diff --git a/faq/faq.rst b/faq/faq.rst
index fbfcb6e..63ea8fc 100644
--- a/faq/faq.rst
+++ b/faq/faq.rst
@@ -180,6 +180,8 @@
   such an issue, please send the fix as pull request and we will be happy to
   merge it.
 
+.. _faq_try_optee:
+
 Q: What is the quickest and easiest way to try OP-TEE?
 ======================================================
     - That would be running it on QEMU on a local PC. To do that you would need to: