Improve the README file (#734)

There is wide spread misconception that in order to build a Maven project
the command is `mvn clean install`.

It would be better to promote the right way (in the vast majority of the cases)
to build a Maven project.

`mvnd verify` aligns with Maven documentation as well,
where the example command is `mvn verify`.

README.adoc

@@ -152,7 +152,7 @@ $ xattr -r -d com.apple.quarantine mvnd-x.y.z-darwin-amd64
 
 [source,shell]
 ----
-mvnd clean install
+mvnd verify
 ----
 
 == `mvnd` specific options