Add three new cities

cities.md

@@ -32,11 +32,14 @@ As a disclaimer, BitDevs NYC has no official associations with or oversight of t
 - [Oslo](https://www.meetup.com/bitcoin-developers-oslo/)
 - [Paris](https://twitter.com/bitdevsfr)
 - [Portland](https://www.meetup.com/portlandbitdevs/)
+- [Porto Alegre](https://poabitdevs.org/)
 - [Raleigh / Durham / Chapel Hill](https://trianglebitdevs.org/)
 - [San Francisco](https://www.sfbitcoindevs.org/)
 - [San Juan](https://sanjuanbitdevs.org/)
+- [San Salvador](https://bitdevelsalvador.com/)
 - [São Paulo](https://bitdevsportugues.org)
 - [Singapore](https://bitdevs.sg/)
+- [Sydney](https://bitcoinsydney.org)
 - [Taipei](https://bitdevs.tw/)
 - [Tampa](https://tampabitdevs.io/)
 - [Vancouver](https://bitdevs.ca/)