Add fuzzing code and readme.md to explain the fuzzer

[asvetlik]

Overview

A fuzzer.go file is being added to fuzz the Bitmap.UnmarshalBinary. A readme.md to explain the fuzzer operations is also being added.

Pull request checklist

• I have read the contributing guide.
• I have agreed to the Contributor License Agreement.
• I have updated the documentation.
• I have resolved any merge conflicts.
• I have included tests that cover my changes.
• All new and existing tests pass.
• Make sure PR title conforms to convention in CHANGELOG.md.
• Add appropriate changelog label to PR (if applicable).

Code review checklist

This is the checklist that the reviewer will follow while reviewing your pull request. You do not need to do anything with this checklist, but be aware of what the reviewer will be looking for.

• Ensure that any changes to external docs have been included in this pull request.
• If the changes require that minor/major versions need to be updated, tag the PR appropriately.
• Ensure the new code is properly commented and follows Idiomatic Go.
• Check that tests have been written and that they cover the new functionality.
• Run tests and ensure they pass.
• Build and run the code, performing any applicable integration testing.
• Make sure PR title conforms to convention in CHANGELOG.md.
• Make sure PR is tagged with appropriate changelog label.

[CLAassistant]

All committers have signed the CLA.

[shaqque]

can we add the -bin, -workdir, and -func flags here to be more explicit? The func and workdir flags are for supporting multiple fuzzing functions, which would each require different corpuses.

[asvetlik]

On pull request #2012, alanbernstein suggested that we clarify that the sample fragments are sample Pilosa fragments and that we provide an example on how to copy the fragments into the workdir/corpus folder. The Provided example on how to copy Pilosa fragments in README.md commit implements these suggestions.

I made the desired changes