Doc block reward change - fix How get doge section

Such commit, verry fix.
So the block reward change seems to have not been updated in the readme, saw there was pull request that were trying to push this to master and was rejected. Hope this is how you want it done.

I had some debate in another cryptocoin and I was blamed for being outdated because I was looking at this section.

Data taken from wikipedia:
http://en.wikipedia.org/wiki/Dogecoin#Block_schedule