Add Washington DC to main locations list

Readme.md

@@ -50,13 +50,14 @@ Want to organize a local NodeBots Day event. You should!
  - [Dallas, Texas, USA](2016/dallas/)
  - [Houston, Texas, USA](2016/houston/)
  - [Los Angeles, California, USA](2016/la)
+ - [Mexico City, Mexico](2016/mexico)
  - [Miami, Florida, USA](2016/miami)
  - [New York City, USA](2016/nyc/)
  - [Norfolk, Virginia, USA](2016/norfolk)
  - [Phoenix/Mesa, Arizona, USA](2016/phoenix)
  - [Sacramento, California, USA](2016/sacramento)
  - [Seattle, Washington, USA](2016/seattle)
- - [Mexico City, Mexico](2016/mexico)
+ - [Washington, DC, USA](2016/washingtondc)
 
 ### Central America
  - [Guatemala City, Guatemala](2016/guatemala/)