docs: Mention Python 3 in the README.
@@ -13,6 +13,8 @@ This repository contains the source code for Zulip's PyPI packages:
* `zulip_botserver`: [PyPI package](https://pypi.python.org/pypi/zulip-botserver)
for Zulip's Flask bot server.
+The source code is written in *Python 3*.
+
## Development
1. Fork and clone the Git repo:
