Improve texttest documentation

Specifically make it easier to test the Java version.
Added a test rig so you can use gradle to run the java version

Java/texttest_rig.py

@@ -0,0 +1,14 @@
+#!/usr/bin/env python
+"""
+This script uses Gradle to execute the TexttestFixture.
+It is designed to be used by TextTest and specified in the file 'texttests/config.gr' in this repo.
+It is more convenient for TextTest to use since Gradle needs
+several arguments in addition to the one the TextTest fixture needs.
+"""
+import os
+import subprocess
+import sys
+
+args = " ".join(sys.argv[1:])
+TEXTTEST_HOME = os.environ.get("TEXTTEST_HOME", os.getcwd())
+subprocess.run(f"{TEXTTEST_HOME}/Java/gradlew -p {TEXTTEST_HOME}/Java -q text --args {args}", shell=True)