AppData additions required for the software center

["Richard Hughes (semi-automated)" <autohughski gmail com>]

Hi again!

First, apologies for the direct email. I'm emailing you directly as you've been listed as the update contact 
in one or more AppData files.

We've been busy building an awesome software center, and we've been adding more and more metadata fields that 
upstream authors can set. The software center is now being used in Fedora, Opensuse, Ubuntu, Debian and Arch, 
with many millions of happy users.

Some of the newest features include a way to make it easy for translators to contribute new translations of 
your applications by specifying a URL in the gnumeric.appdata.xml AppData file that tells them where to start 
looking. This can be specified by adding:

<url type="translate">http://the-web-site-with-translation-instructions/</url>

Another useful tag to add is to tell end-users where to donate, for instance:

<url type="donation">http://www.gnome.org/friends/</url>

If it's been some time since you updated the AppData file (and hey, you've got an app to write!) you can get 
add the latest metadata fields by doing `appstream-util upgrade gnumeric.appdata.xml` and then replacing any 
FIXMEs in the file with actual data. We'll be putting more functionality into the software center in the 
future that uses this extra data, but we need more upstream software to opt-in before we can enable features, 
for instance, providing a button for users to donate to specific apps.

You can also use `appstream-util validate-relax` on your AppData file to check the various fields meet our 
style guidelines. If you disagree with any of the validation warnings, please let me know!

Of course, you don't have to do a release with these enhancements straight away, and if you have a stable 
branch it would be a good thing to backport this as well if it does not add translated strings or you have no 
string freeze policy.

When you've changed the file(s) and committed, please email me back and I'll mark your application as 
completed. If you don't want to hear from me ever again just edit the <update_contact> in the AppData file 
and change it to somebody else. I'm not planning on emailing more than once every 6 months, so don't worry 
about me spamming you with even more work to do.

Thanks,

Richard