Add checkstyle info on CONTRIBUTING.md (#1290)

Signed-off-by: Matheus Cruz <matheuscruz.dev@gmail.com>
Co-authored-by: artur-ciocanu <artur.ciocanu@gmail.com>

Author: mcruzdev

CONTRIBUTING.md

@@ -56,13 +56,25 @@ This section describes the guidelines for contributing code / docs to Dapr.
 All contributions come through pull requests. To submit a proposed change, we recommend following this workflow:
 
 1. Make sure there's an issue (bug or proposal) raised, which sets the expectations for the contribution you are about to make.
-1. Fork the relevant repo and create a new branch
-1. Create your change
+2. Fork the relevant repo and create a new branch
+3. Create your change
     - Code changes require tests
-1. Update relevant documentation for the change
-1. Commit and open a PR
-1. Wait for the CI process to finish and make sure all checks are green
-1. A maintainer of the project will be assigned, and you can expect a review within a few days
+4. Update relevant documentation for the change
+5. Check the code style
+6. Commit and open a PR
+7. Wait for the CI process to finish and make sure all checks are green
+8. A maintainer of the project will be assigned, and you can expect a review within a few days
+
+### Configure the code style with checkstyle
+
+The project contains a checkstyle file (`checkstyle.xml`) that must be used for formatting the code.
+
+* IntelliJ IDEA
+   You can use [CheckStyle-IDEA plugin](https://plugins.jetbrains.com/plugin/1065-checkstyle-idea).
+* VSCode
+   You can use [Checkstyle for Java](https://marketplace.visualstudio.com/items?itemName=shengchen.vscode-checkstyle).
+* Eclipse
+  You can use [Eclipse Checkstyle Plugin](https://checkstyle.org/eclipse-cs/#!/)
 
 #### Use work-in-progress PRs for early feedback