editorial fixes in the readme

# Test project for titan-binaries

This folder contains a dummy TTCN project to show how to use the Docker image titan-binaries

in your toolchain.

The first line referers to the base image to use, in this case titan-binaries.

Note: You need titan-binaries to build the image locally before you can use it.

The second line adds your source directory into the container, so that it can be

built and run within the containerized environment.