[draft] two QA tips "choose URIs wisely" and "managing URIs"

Hi,

I have a long overdue action item to replace the "Cool URIs don't 
change" link to an actual (standard formatted etc.) QA Tip. In order to 
keep Tips short enough I chose to split the tip into a "choosing" URI 
part and a "managing" part.

Choose URIs wisely <http://www.w3.org/QA/Tips/uri-choose>
Managing URIs <http://www.w3.org/QA/Tips/uri-manage>

I had started writing them a while ago and only did a sufficient 
cleanup recently. In the meantime Victor contributed a good Tip on 
making URIs readable, but I don't think it should be problematic: the 
scope of the Tips vary, and we're not trying to build a prefectly 
consistent document but a collection of useful tidbits. This doesn't 
mean these two new draft tips are perfect, on the contrary, input would 
be greatly appreciated.

Thanks.
-- 
olivier