create docs when for sitemap generation [SeoBundle]

[ElectricMaxxx]

... when symfony-cmf/seo-bundle#196 is ready.

[dbu]

The code is merged. Now its time to write the docs. best we do it while we still remember what we did in the code :-) But i think to use the sitemap is a lot easier than to build it...

[ElectricMaxxx]

yea btw: there are 3 more features missing to document them:

• error handling [SeoBundle][error handling] Docs for error handling #606
• alternate language create docs for alternate language support in the SeoBundle #605

Can be a kind of procastination from my side, but i think i do not have the skills to write docs :-(
BUT i will try to start them in the evening, so somebody else can fix them.

[dbu]

see #683