Creating giveaways with links to sponsorship/charity donations?

I'm doing a half-marathon in September and I was thinking about using it to raise money for charity - I would probably choose an animal related one, either a local shelter or something with national or international reach.

And so I was wondering whether it would be allowed for me to include links to my fundraising page(s) with giveaways I create here on SteamGifts. Obviously I couldn't and wouldn't require donations in exchange for giveaway entries, and I wouldn't be asking people to send me money directly - I would be using a charity fundraising website such as JustGiving - so is it okay for me to use the description to talk about the charity and include links to said page? I've seen people do similar things before but just wanted to clarify that it's not against the rules.