Merge pull request #416 from silvin-lubecki/experimental-readme

Add some documentation about experimental build.

README.md

@@ -295,4 +295,17 @@ $ source <(docker-app completion zsh)
 Set the docker-app completion code for zsh to autoload on startup in your ~/.zshrc
 ```sh
 source <(docker-app completion zsh)
-```
+```
+
+## Experimental
+
+Some commands are flagged as experimental and will remain in this state until they mature. These commands are only accessible using an experimental binary. Feel free to test these commands and give us some feedback!
+
+### How to build your own experimental binary
+
+```console
+$ make EXPERIMEMTAL=on bin/docker-app
+$ ./bin/docker-app version
+...
+Experimental: on
+```