[tests] Simplify instructions to use the docker test runner (#656)

Author: labbati

README.md

@@ -76,17 +76,12 @@ Now you are in a bash shell. You can now run tests as you would do in your local
 
     $ tox -e '{py35,py36}-redis{210}'
 
-If you are in a unix machine, we also provide a shell script to execute commands in the provided container (so you don't
-forget to remove-`--rm` the container after you run it).
+We also provide a shell script to execute commands in the provided container.
 
 For example to run the tests for `redis-py` 2.10 on Python 3.5 and 3.6:
 
     $ ./scripts/ddtest tox -e '{py35,py36}-redis{210}'
 
-You can also add the `scripts` folder to your path, so then you can run
-
-    $ ddtest tox -e '{py35,py36}-redis{210}'
-
 
 ### Continuous Integration
 
@@ -115,4 +110,3 @@ When two or more approaches must be compared, please write a benchmark in the
 of the algorithm. To run your benchmark, just:
 
     $ python -m tests.benchmark
-