[Docs] Need to add suppressions instruction to readme for configuring IntelliJ checkstyle rules

On the main Pulsar Github readme, in the section of configuring Checkstyle rules in IntelliJ (https://github.com/apache/pulsar#configure-checkstyle)

I noticed that there's a suppressions.xml file in the same directory as the checkstyle.xml file:

After following the instructions to select the checkstyle.xml file, this additional dialog box opens:

Should we be providing the path to the suppressions.xml file as the value in that box? If so, is that an absolute or a relative path?
Additional instructions on this would be helpful.

Open the main README at the Configure Checkstyle rules in IntelliJ section and inspect the instructions around checkstyle.xml. Review the accompanying suppressions.xml file and determine the path format IntelliJ expects for the additional dialog. Update the README with the suppressions guidance and verify that the setup steps are complete.

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