Add entrypoint (#94)

* Add entrypoint

* entrypoint can be empty

Author: davidkopp

content/en/docs/measuring/usage-scenario.md

@@ -125,6 +125,10 @@ services:
       + Defaults to `/tmp/repo`
     - `command:` **[str]** *(optional)*
       + Command to be executed when container is started. When container does not have a daemon running typically a shell is started here to have the container running like `bash` or `sh`.
+    - `entrypoint:` **[str]** *(optional)*
+      + Declares the default entrypoint for the service container. This overrides the ENTRYPOINT instruction from the service's Dockerfile.
+      + The value of `entrypoint` can either be an empty string (ENTRYPOINT instruction will be ignored) or a single word (helpful to provide a script).
+      + If you need an entrypoint that consists of multiple commands/arguments, either provide a script (e.g. `entrypoint.sh`) or set it to an empty string and provide your commands via `command`.
     - `shell:` **[str]** *(optional)*
       + Will execute the `setup-commands` in a shell. Use this if you need shell-mechanics like redirection `>` or chaining `&&`.
       + Please use a string for a shell command here like `sh`, `bash`, `ash` etc. The shell must be available in your container