add build readme

build/README.md

@@ -0,0 +1,16 @@
+# blob-domain
+
+[![Build Status](https://travis-ci.org/Blobfolio/blob-domain.svg?branch=master)](https://travis-ci.org/Blobfolio/blob-domain)
+
+blob-domain uses the [Public Suffix List](https://publicsuffix.org/list/) to construct and validate the suffix portion of a domain name.
+
+This repository will be updated monthly, but if you need more up-to-date sources, you can recompile the database files locally by running the included build script:
+
+```php
+//run it in the terminal of your choice:
+php build/build.php
+```
+
+This will store local copies of the data it retrieves in `build/src`.
+
+An updated `lib/blobfolio/domain/data.php` file will be generated at the end of the build process.