Clarify promesa

Author: borkdude

README.md

@@ -579,7 +579,7 @@ user=> (pprint/pprint (process "ls"))
 
 ### Promesa
 
-You can combine this library with [promesa](https://github.com/funcool/promesa)
+On the JVM (not in bb), you can combine this library with [promesa](https://github.com/funcool/promesa)
 in the following way. This requires `:exit-fn` which was released in version
 `0.2.10`.