Update README.md

README.md

@@ -15,6 +15,7 @@ A project or branch of a project on GitHub can be checked out in multiple direct
 - [lively4-core](https://lively-kernel.org/lively4/lively4-core/start.html)
 - [lively4-stable](https://lively-kernel.org/lively4/lively4-stable/start.html)
 - [lively4-jens](https://lively-kernel.org/lively4/lively4-jens/start.html)
+- [aexpr](https://lively-kernel.org/lively4/aexpr/start.html)
 
 The Lively4 server and GitHub sync tools can check out arbitrary projects, such as the code of [lively4-server](https://lively-kernel.org/lively4/lively4-server/) itself, or the source of a paper hosted by overleaf.
 
@@ -35,4 +36,4 @@ The Lively4 server and GitHub sync tools can check out arbitrary projects, such
 
   - Reactive Programming [RP 2018](https://lively-kernel.org/lively4/lively4-seminars/RP2018/index.md)
 
-### [Imprint](imprint.md)
+### [Imprint](imprint.md)