Add missing link for the codesearch.

Author: Dor1s

lessons/12/README.md

@@ -18,6 +18,7 @@ Once you find a bug with it, submit your fuzzer to [Chrome Fuzzer Program].
 
 [Chromium]: https://www.chromium.org/developers/how-tos/get-the-code
 [Chrome Fuzzer Program]: https://www.google.com/about/appsecurity/chrome-rewards/index.html#fuzzerprogram
+[Codesearch]: https://cs.chromium.org/
 [build existing fuzzers]: https://chromium.googlesource.com/chromium/src/+/master/testing/libfuzzer/reproducing.md#Reproducing-LibFuzzer-ASan-bugs
 [existing targets]: https://cs.chromium.org/search/?q=LLVMFuzzerTestOneInput&sq=package:chromium&type=cs
 [new ones]: https://cs.chromium.org/search/?q=file:.*%5C.h+%22const+uint8_t*%22&sq=package:chromium&type=cs