Extend README and add section on testing

README.md

@@ -2,4 +2,26 @@
 
 This directory contains concordance lists for accepted values. Where e.g. an entry type may be identified at museum-digital only by its ID, it is not realistic to expect providers of import data (which is to say: museums) to enter the entry type ID from museum-digital's relevant list. Hence, the lists contained in this subdirectory provide human-readable names for the IDs accepted by museum-digital as found in previous imports, so that they can be automatically translated to the IDs and names as used within the context of museum-digital.
 
-The lists are grouped as class constants of their relevant entry type. All class names may be prefixed with _MDConc_.
+The lists are grouped as (private) class constants of their relevant entry type.
+
+- All class names may be prefixed with _MDConc_.
+- All concordance list classes implement the MDImporterConcordanceListInterface interface.
+  - They can thus all be used using a static function `getConcordanceTarget(string $input)`. E.g.:
+    ```
+    $checkType = MDConcCheckTypes::getConcordanceTarget("Vollständigkeit");
+    ```
+- All concordance lists can be found directly in the `[/src](./src)` directory.
+
+## Environment and Purpose for Using a Separate Subrepository
+
+This repository is intended to be used as a subrepository of MDImporter. Its full functionality is thus only available with the inclusion of some other subrepositories provided in the context of the importer (e.g. MDAllowedValueSets).
+
+Editing can be done by simply adding to the lists however. It is hoped, that the publication of this subrepository as a standalone repository makes this process easier. Just clone this repository and enter the missing values in the relevant classes in the `[/src](./src)` directory.
+
+## Testing
+
+Tests exist to ensure that all concordance lists implement the MDImporterConcordanceListInterface interface and throw an MDImporterMissingConcordance exception, if a new, yet unknown value is encountered. If this repository is set up as part of an installation of the MDImporter, they can be run using:
+
+```
+phpunit tests
+```