Various updates to Readme
Various updates to Readme

* Included bower + npm/browserify installation instructions.
* Included code snippet for npm/browserify usage.
* Updated Domains/TLDs to latest in mailcheck.js.
* Domains/TLDs -> Unordered-list for easier scanning.
* Included explicit instructions on how to replace or extend the existing Domains/TLDs
* Some whitespace & consistency fixes.
mailcheck/mailcheck,nacho87/mailcheck,vladikoff/mailcheck,giovaniharyadi/mailcheck,archiveds/mailcheck,mcanthony/mailcheck,gmac/mailcheck,archiveds/mailcheck,mailcheck/mailcheck,giovaniharyadi/mailcheck,mcanthony/mailcheck,mcanthony/mailcheck,gmac/mailcheck,mailcheck/mailcheck,vladikoff/mailcheck,Shopify/mailcheck,nacho87/mailcheck,archiveds/mailcheck,vladikoff/mailcheck,nacho87/mailcheck,giovaniharyadi/mailcheck,gmac/mailcheck