Add Reproducible Builds badge to README (#333)

README.md

@@ -20,6 +20,7 @@ loves Error Prone: producing high-quality and consistent Java
 code_][picnic-blog-ep-post].
 
 [![Maven Central][maven-central-badge]][maven-central-search]
+[![Reproducible Builds][reproducible-builds-badge]][reproducible-builds-report]
 [![GitHub Actions][github-actions-build-badge]][github-actions-build-master]
 [![License][license-badge]][license]
 [![PRs Welcome][pr-badge]][contributing]
@@ -226,3 +227,5 @@ guidelines][contributing].
 [refaster]: https://errorprone.info/docs/refaster
 [refaster-rules-bigdecimal]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/BigDecimalRules.java
 [refaster-rules]: https://github.com/PicnicSupermarket/error-prone-support/blob/master/error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/
+[reproducible-builds-badge]: https://img.shields.io/badge/Reproducible_Builds-ok-success?labelColor=1e5b96
+[reproducible-builds-report]: https://github.com/jvm-repo-rebuild/reproducible-central/blob/master/content/tech/picnic/error-prone-support/error-prone-support/README.md