doc: updated changelog and credits.

CREDITS.md

@@ -44,5 +44,7 @@ Contributors to Magnum library
     packages
 -   Alexander F Rødseth ([@xyproto](https://github.com/xyproto)) -- packages in
     the ArchLinux community repository
+-   Nathan Ollerenshaw ([@matjam](https://github.com/matjam)) --- Ubuntu
+    packages in a PPA repository
 
 Big thanks to everyone involved!

doc/changelog.dox

@@ -55,6 +55,11 @@ See also:
 -   @ref Platform::GlfwApplication no longer stores a needless global window
     pointer
 
+@subsection changelog-latest-buildsystem Build system
+
+-   There's now a PPA for Ubuntu packages. See @ref building-packages-deb
+    for more information.
+
 @subsection changelog-latest-bugfixes Bug fixes
 
 -   An assert was firing during @ref Platform::GlfwApplication initialization