Better advice for skipping tests in README.md (#4157)

This causes test artifacts to be built even though tests are not run.

Signed-off-by: Jesse Wilson <jwilson@squareup.com>

README.md

@@ -40,7 +40,7 @@ The first build may take a longer than expected as Maven downloads all the depen
 
 The build tests do a lot of stress testing, and on some machines it is necessary to set the file descriptor limit to greater than 2048 for the tests to all pass successfully.
 
-It is possible to bypass tests by building with `mvn -Dmaven.test.skip=true install` but note that this will not produce some of the test jars that are leveraged in other places in the build.
+It is possible to bypass tests by building with `mvn clean install -DskipTests`.
 
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