Add FAQ to the documentation

Allow us to use different words to describe certain features to
make it easier for people to find it using their own vocabulary.
Without the need to sneak in the documentation all the possible words.

e.g. In this case searching for "exclude" could not help the
user as that word was not used in our documentation.

See rust-lang#2218

Author: szabgab

guide/src/SUMMARY.md

@@ -38,6 +38,7 @@
     - [Preprocessors](for_developers/preprocessors.md)
     - [Alternative Backends](for_developers/backends.md)
 
+- [FAQ](faq.md)
 -----------
 
 [Contributors](misc/contributors.md)

guide/src/faq.md

@@ -0,0 +1,7 @@
+# FAQ - Frequently Asked Questions
+
+
+## Exclude pages from the search bar
+
+See the [configuration of the HTML renderer](./format/configuration/renderers.html#outputhtmlsearchchapter).
+