Move FUZZING.md to the top level

Though the fuzzing tests are in the tests directory, we should move
the FUZZING.md file itself to the toplevel to make it more visible.

Signed-off-by: Brad House (@bradh352)

.reuse/dep5

@@ -9,7 +9,7 @@ Copyright: The c-ares project and its contributors.
 License: MIT
 
 # Docs
-Files: AUTHORS CONTRIBUTING.md GIT-INFO README.md README.msvc RELEASE-PROCEDURE.md RELEASE-NOTES.md FEATURES.md SECURITY.md DEVELOPER-NOTES.md INSTALL.md test/README.md test/FUZZING.md src/lib/include/README.md src/lib/thirdparty/apple/README.md
+Files: AUTHORS CONTRIBUTING.md GIT-INFO README.md README.msvc RELEASE-PROCEDURE.md RELEASE-NOTES.md FEATURES.md SECURITY.md DEVELOPER-NOTES.md INSTALL.md FUZZING.md test/README.md src/lib/include/README.md src/lib/thirdparty/apple/README.md
 Copyright: The c-ares project and its contributors.
 License: MIT