Update junit.md

Author: sunshowers

site/src/book/junit.md

@@ -16,6 +16,13 @@ Some notes about the JUnit support:
 * Every test binary forms a single `<testsuite>`. Every test forms a single `<testcase>`.
 * Standard output and standard error are included for failed and retried tests. (However, [invalid XML characters](https://en.wikipedia.org/wiki/Valid_characters_in_XML) are stripped out.)
 
+## Post-processing
+
+Some tools that read JUnit files don't follow the Jenkins standard. You can post-process the JUnit file in such cases. Here's some recommendations for post-processing tools written by community members:
+* CircleCI: [`circleci-junit-fix`](https://github.com/conradludgate/circleci-junit-fix).
+
+## Example
+
 Here's an example JUnit file generated by `cargo-nextest`.
 
 ```xml