[incubator-kie-drools-6386] Update note about mvel deprecation (#4569)

Author: tkobayas

drools-docs/src/modules/ROOT/pages/migration-guide/_nonexec-model-to-exec-model.adoc

@@ -23,6 +23,11 @@ The `drools-engine-classic` and `drools-mvel` execute rules with `non executable
 
 As mentioned, `drools-engine-classic` and `drools-mvel` are deprecated, it is recommended to migrate from a `non-executable model` to an `executable model` by changing dependencies.
 
+[NOTE]
+====
+`drools-mvel` is deprecated, but `drools-mvel-parser` and `drools-mvel-compiler` are not deprecated.
+====
+
 In general, from an external perspective, rule evaluation and rule consequence execution results can be expected to be the same using either the `non-executable` model or the `executable model`. You may however encounter a few edge cases during compile time or runtime. If you find any issues, please report them to the {PRODUCT} community. We have already identified some small known differences, reported below.
 
 === Invalid cast