- Don't explicitly mention "ES5" in https://mozilla.github.io/pdf.js/getting_started/#download, since that's no longer accurate. As-is, this will more than likely give users the wrong impression regarding our *actual* browser support.
- Reword the "Getting the Code"-section of the README, since an ES6-compatible browser is no longer sufficient for development purposes given our usage of modern ECMAScript features.
- Update the "Building PDF.js"-section of the README, to explicitly mention both the `gulp generic` and `gulp generic-es5` commands.
Hopefully this will help reduce *some* user confusion, but we should perhaps also consider changing the "-es5"-suffix in our build-scripts and build-folders. (That would however require coming up with a "better" suffix, which might not be trivial.)
adding commas each in two sentences in order to make readers fully understand when reading index.md and to organize the context properly based on grammatical rules.
Also updates a `console.log` statement in the `gulp importl10n` command (since I forgot it in a previous patch, and it didn't seem necessary with a separate patch for it).
