Update SUMMARY.md

Author: gustavo-grieco

SUMMARY.md

@@ -80,6 +80,7 @@
       - [How to test bytecode-only contracts](./program-analysis/echidna/advanced/testing-bytecode.md)
       - [How to use hevm cheats to test permit](./program-analysis/echidna/advanced/hevm-cheats-to-test-permit.md)
       - [How to seed Echidna with unit tests](./program-analysis/echidna/advanced/end-to-end-testing.md)
+      - [How to fuzz contracts with external libraries](./program-analysis/echidna/advanced/working-with-libraries.md)
       - [Understanding and using `multi-abi`](./program-analysis/echidna/advanced/using-multi-abi.md)
     - [Fuzzing tips](./program-analysis/echidna/fuzzing_tips.md)
     - [Frequently Asked Questions](./program-analysis/echidna/frequently_asked_questions.md)