chore: don't pack `example/` and `test/` folders and other dev files

[mvayngrib]

currently this package includes many files that aren't needed at runtime. This PR npmignores them

Test Plan

run npm pack. You should see only these files packed

npm notice === Tarball Contents === 
npm notice 592B   .github/FUNDING.yml            
npm notice 6.6kB  CHANGELOG.md                   
npm notice 1.1kB  LICENSE                        
npm notice 4.1kB  README.md                      
npm notice 2.1kB  index.js                       
npm notice 38.8kB json-stable-stringify-1.0.2.tgz
npm notice 2.0kB  package.json       

[mvayngrib]

@ljharb thanks for the quick response! Could u elaborate on why that's necessary? I imagine this can bloat node_modules quite a bit for other projects (maybe not json-stable-stringify/jsonify specifically). Can't the consumers who want to check tests clone the github repo and check out the tag (and compare files to npm contents if they really need to)?

[ljharb]

I don't particularly care about bloated node_modules; disk space is infinite and free.

Cloning the repo requires an internet connection, and, since repos are mutable (like this package's original repo), not guaranteed to exist at all.

[mvayngrib]

haha understood. What brought me here was actually a different reason. We audit all lines of code that make it to build machines, so this made audit pretty painful. Your module your choice of course

[ljharb]

That seems like a really impractical policy, given that tons of code will exist in node_modules that doesn't end up in production, and is thus irrelevant.