ProjectExplorer: Document source of test data for testAbiOfBinary_data

Change-Id: I2e9b59d5ac99de0bbb9cf1f64210439e41f403af
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/valgrind/valgrindmemcheckparsertest.cpp

@@ -114,6 +114,7 @@ static QString dataFile(const QString &file)
 
 static QString extraDataFile(const QString &file)
 {
+    // Clone test data from: https://git.qt.io/chstenge/creator-test-data
     static QString prefix = QString::fromLocal8Bit(qgetenv("QTC_TEST_EXTRADATALOCATION"));
     if (prefix.isEmpty())
         return QString();