Warn about plain text specifics in AppendToTextFile.java (#4097)

See #4092

rewrite-core/src/main/java/org/openrewrite/text/AppendToTextFile.java

@@ -72,7 +72,11 @@ public String getDisplayName() {
 
     @Override
     public String getDescription() {
-        return "Appends or replaces content of an existing plain text file, or creates a new one if it doesn't already exist.";
+        return "Appends or replaces content of an existing plain text file, or creates a new one if it doesn't already exist. " +
+               "Please note that this recipes requires existing plain text files' format to be successfully parsable by OpenRewrite. " +
+               "If a file is left unchanged, it might be parsed as a `Quark` rather than plain text. In such case, use the `plainTextMask` option. " +
+               "See the [Gradle](https://docs.openrewrite.org/reference/gradle-plugin-configuration#configuring-the-rewrite-dsl) or " +
+               "[Maven](https://openrewrite.github.io/rewrite-maven-plugin/run-mojo.html#plainTextMasks) plugin configuration page.";
     }
 
     @Override