Add api.ai in Machine Learning category

README.md

@@ -269,6 +269,7 @@ For information on contributing to this project, please see the [contributing gu
 | Cleverbot | Web chat bot | `apikey` | Yes | [Go!](https://www.cleverbot.com/api/) |
 | Unplugg | Forecasting API for timeseries data | `apikey` | Yes | [Go!](https://unplu.gg/test_api.html) |
 | Wit.ai | Natural Language Processing | `OAuth` | Yes | [Go!](https://wit.ai/) |
+| api.ai | Natural Language Processing | `apikey` | Yes | [Go!](https://api.ai/) |
 
 ### Math