[libFuzzer] fix MojoLPM link in the documentation.

TBR=markbrand@google.com,mbarbella@chromium.org

Change-Id: I19c360fcf8638135eac3d1ee0eed9e4a4d882a20
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2268838Reviewed-by: Martin Barbella <mbarbella@chromium.org>
Reviewed-by: Max Moroz <mmoroz@chromium.org>
Commit-Queue: Max Moroz <mmoroz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#782748}

testing/libfuzzer/README.md

@@ -66,6 +66,7 @@ Started Guide].
 [Creating a fuzz target that expects a protobuf]: libprotobuf-mutator.md
 [Detailed references]: reference.md
 [Fuzzing]: https://en.wikipedia.org/wiki/Fuzzing
+[Fuzzing mojo interfaces]: ../../mojo/docs/mojolpm.md
 [Getting Started Guide]: getting_started.md
 [Guided in-process fuzzing of Chrome components]: https://security.googleblog.com/2016/08/guided-in-process-fuzzing-of-chrome.html
 [Improving fuzz target efficiency]: efficient_fuzzing.md