Merge pull request #149 from rage/merge-change

documented the course-wide config file

Author: Heliozoa

docs/tmcproject.md

@@ -1,4 +1,4 @@
-Exercises can be configured by adding an optional `.tmcproject.yml` file to the exercise root directory.
+Exercises can be configured by adding an optional `.tmcproject.yml` file to the exercise root directory. Additionally, a course-wide file can be added to the course's root. When the course is then refreshed, the course-wide file is merged with the exercise-specific ones for the exercise stub and solution. For each key-value pair in the course-wide file, if the key is not present in the exercise-specific file, it is added to it with the course-wide file's value.
 
 ## Keys
 
@@ -13,7 +13,7 @@ All of the keys listed below are optional.
 | no-tests               | Boolean OR Map "points" -> List of string OR integer | If set to true or a map, the no-tests plugin is used for the exercise. If set to a list, the list will be used as the exercise's points.                                             |
 | fail_on_valgrind_error | Boolean                                              | If set, the C plugin will attempt to run valgrind and fail the exercise if it discovers errors.                                                                                      |
 | minimum_python_version | Python version string                                | Must be "{major}.{minor}.{patch}", "{major}.{minor}" or "{major}". If set, the Python plugin will warn the user if the Python version being used is below the given minimum version. |
-| sandbox_image | The Docker image that should be used at the sandbox. | Should be a URL. |
+| sandbox_image          | The Docker image that should be used at the sandbox. | Should be the Docker registry path of the image.                                                                                                                                     |
 
 ## Example file contents