* Explain how to run full tests

packages/fcl-jsonschema/tests/README.md

@@ -0,0 +1,18 @@
+# JSON-Schema testsuite.
+
+The default tests test all parts.
+
+However, it is possible to extend the testsuite by pointing the binary to
+the test directory of the JSON-Schema.org testsuite.
+
+You can obtain these by cloning the official testsuite:
+
+[https://github.com/json-schema-org/JSON-Schema-Test-Suite](https://github.com/json-schema-org/JSON-Schema-Test-Suite)
+
+git clone https://github.com/json-schema-org/JSON-Schema-Test-Suite.git
+
+and then run the testsuite with the --test-dir argument:
+```
+./testschema --testdir=JSON-Schema-Test-Suite/tests/draft2020-12
+```
+