As of right now the only way to earn Pokecoins is to control a gym or to buy them with cold hard cash. Each gym you control grants you 10 gold and 500 stardust but you can only control up to 10 gyms at a time to reap this reward! (Any gyms controlled past 10 will just be to show domination 😉 ) Make sure to collect your rewards as soon as you place your Pokémon at a gym. They can be collected in the top right portion of the shop (As pictured below). Make sure to check back every 21 hours as it resets and you can collect more gold as long as you control it.