Update Soy templates page to use type-safe @param

Type-safe template parameters are awesome and it's one of the things that really differentiates soy templates from the competition. I hope you'll consider merging my patch, because I think it'd be really awesome if we could encourage people to use this amazing feature.

Thanks in advance <3
Merge pull request #5 from jart/patch-1

Update Soy templates page to use type-safe @param