FAQ: added two questions

They are from README.md.

(In a latter commit they would be removed from README.md consequently)

doc/FAQ.org

@@ -9,6 +9,8 @@
   - [[#environment-variables-or-path-are-not-set-properly][Environment variables or PATH are not set properly]]
   - [[#how-to-fix-package-download-errors-when-installing-spacemacs-][How to fix package download errors when installing Spacemacs ?]]
   - [[#how-to-fix-symbols-value-as-variable-is-void-errors-on-startup][How to fix =Symbol's value as variable is void= errors on startup?]]
+  - [[#how-to-fix-error-package-package-build--is-unavailable][How to fix =error: Package 'package-build-' is unavailable=?]]
+  - [[#how-to-fix-warning-bytecomp-and-other-compilation-warnings][How to fix =Warning (bytecomp)= and other compilation warnings?]]
   - [[#how-to-fix-wrong-type-argument-arrayp-nil-errors-on-startup][How to fix =(wrong-type-argument arrayp nil)= errors on startup?]]
   - [[#the-spacemacs-banner-is-ugly-what-should-i-do][The Spacemacs banner is ugly, what should I do?]]
   - [[#the-powerline-separators-are-ugly-how-can-i-fix-them][The powerline separators are ugly, how can I fix them?]]
@@ -110,6 +112,14 @@ to do this:
 - Set the variable =dotspacemacs-elpa-https= to =nil= in your dotfile. This has
   the same effect as =--insecure=, but is persistent.
 
+** How to fix =error: Package 'package-build-' is unavailable=?
+This may occur due to heavy network traffic. You can fix it by setting the
+=dotspacemacs-elpa-timeout= variable to =70= in your =dotspacemacs= file.
+
+** How to fix =Warning (bytecomp)= and other compilation warnings?
+They are perfectly normal. If you're curious, you can find out why these occur
+[[https://github.com/quelpa/quelpa/issues/90#issuecomment-137982713][here]].
+
 ** How to fix =(wrong-type-argument arrayp nil)= errors on startup?
 This is most likely caused by a corrupted package archive. Try deleting your
 =~/.emacs.d/elpa/archives/= folder and restart Emacs.