Add README.md for GVT specific application.conf

gvt-validation-jar/README.md

+# GVT configuration file
+
+## Context
+
+The GVT dependency:
+
+```xml
+  <dependency>
+    <groupId>gov.nist</groupId>
+    <artifactId>hl7-v2-validation</artifactId>
+    <version>${hl7.v2.version}</version>
+  </dependency>
+```
+can be used with a configuration file in `src/main/resource/application.conf` that overwrite the `reference.conf` found here (<https://github.com/usnistgov/v2-validation/blob/features/v1_6_3/validation/src/main/resources/reference.conf>).
+
+It allows to change level of classification (error, warning, etc.) or message for specific category (single-code-failure, code-not-found-cs-empty, etc.) 
\ No newline at end of file

gvt-validation-jar/src/main/resources/application.conf

-# Add here custom error levels
+# Add here custom error levels or custom message
 report {
 
   code-not-found-cs-empty {