Merge pull request #20866 from suiyuan2009/20801-add-ubuntu-notice

add ubuntu arch note

docs/installation/linux/ubuntulinux.md

@@ -85,7 +85,8 @@ packages from the new repository:
 
             deb https://apt.dockerproject.org/repo ubuntu-wily main
 
-    > **Note**: Docker does not provide packages for all architectures. To install docker on
+    > **Note**: Docker does not provide packages for all architectures. You can find
+	> nightly built binaries in https://master.dockerproject.org. To install docker on
     > a multi-architecture system, add an `[arch=...]` clause to the entry. Refer to the
     > [Debian Multiarch wiki](https://wiki.debian.org/Multiarch/HOWTO#Setting_up_apt_sources)
     > for details.