Browser does not work because gnomad.js is missing

[nabramovs]

Browser does not work because gnomad.js file is missing in the repository.

For those who want to use gnomAD browser before this will be fixed: 1) Download gnomad.js from gnomad.broadinstitute.org 2) Place it in the static folder (gnomad_browser/static/) of your local copy of the browser

[gungorbudak]

Because the file can be bundled from the sources, so follow this:

cd gnomad/
npm install
npm run build

These commands should install dependencies for building gnomad.js and putting it to the right place.

[nawatts]

125 adds documentation for building gnomad.js to the README.