Ubuntu 16.04: apt build-dep option, couple other notes

Mention that apt build-dep can probably be used instead of all the apt install
commands.  Round disk usage values.  Add note to remove statement about testing
if people feel like making an update without testing.

ubuntu16.04.html

@@ -11,10 +11,20 @@
 <h1><a href="index.html"><img src="wayland.png" alt="Wayland logo"></a>
 Building Weston on Ubuntu 16.04</h1>
 
-<p>The following sequence of commands successfully built Weston and
-XWayland on a pristine Ubuntu 16.04 system, on August 16, 2016. These
-commands will probably work on any system based on Ubuntu 16.04.  1,938 MB used
-with documentation dependencies, probably 538 MB used without them.</p>
+<p>The following sequence of commands successfully built Weston and XWayland on
+a pristine Ubuntu 16.04 system, on August 16, 2016. These commands will
+probably work on any system based on Ubuntu 16.04.  ~2 GB used with
+documentation dependencies, ~500 MB used without them.</p>
+
+<!--
+A note to people updating this page:  If this needs an update, and you don't
+feel like going through verification on a pristine install, I encourage you to
+make the needed changes, and just remove the bit above about testing.
+-->
+
+<p>All the "apt install" commands can probably be replaced by just running
+"sudo apt build-dep wayland weston wayland-protocols libinput
+xserver-xorg".</p>
 
 <p>"make check" runs included tests, and is not required, but is a good
 habit.</p>