Removes unneeded sudo, adds clean slate in demo

The sudo to recursively copy the target files from bob's machine
to carl's machine is actually not needed.
This commit removes it from the demo/README.md

The commit also adds a section to the README that explains how
to use the run_demo script to clean all files delated during the
demo which is necessary to re-run the demo.

demo/README.md

@@ -141,7 +141,7 @@ the package for the user.
 
 ```shell
 # Bob has to send the update sources to Carl so that he can package them
-sudo cp -r demo-project ../functionary_carl/ # XXX Might require sudo because of certain .git objects
+cp -r demo-project ../functionary_carl/
 ```
 
 ### Package (Carl)
@@ -234,13 +234,18 @@ supply chain. More complex software supply chains that contain more steps can be
 created in a similar way. You can read more about what in-toto protects against
 and how to use it on [in-toto's Github page](https://in-toto.github.io/).
 
+### Clean slate
+If you want to run the demo again, you can use the following script to remove all the files you created above.
+
+```shell
+cd .. # You have to be the demo directory
+python run_demo.py -c
+```
+
 ### Tired of copy-pasting commands?
-We provide a `run_demo.py` script that sequentially executes all commands
-listed above. Just change into the `demo` directory, run it and observe the
-output.
+The same script can be used to sequentially execute all commands listed above. Just change into the `demo` directory, run `python run_demo.py` without flags and observe the output.
 
 ```shell
-# Being in in-toto root
-cd demo
+# In the demo directory
 python run_demo.py
 ```