document existence of contributed extension functions (#348)

* document existence of contributed extension functions

* Add a link to the extension functions

Co-authored-by: Ophir LOJKINE <ophir.lojkine@auto-grid.com>

README.md

@@ -5,7 +5,7 @@
 
 For the impatients, try the demo here: http://kripken.github.io/sql.js/examples/GUI
 
-*sql.js* is a port of [SQLite](http://sqlite.org/about.html) to Webassembly, by compiling the SQLite C code with [Emscripten](http://kripken.github.io/emscripten-site/docs/introducing_emscripten/about_emscripten.html). It uses a [virtual database file stored in memory](https://kripken.github.io/emscripten-site/docs/porting/files/file_systems_overview.html), and thus **doesn't persist the changes** made to the database. However, it allows you to **import** any existing sqlite file, and to **export** the created database as a [JavaScript typed array](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Typed_arrays).
+*sql.js* is a port of [SQLite](http://sqlite.org/about.html) to Webassembly, by compiling the SQLite C code with [Emscripten](http://kripken.github.io/emscripten-site/docs/introducing_emscripten/about_emscripten.html), with [contributed math and string extension functions](https://www.sqlite.org/contrib?orderby=date) included. It uses a [virtual database file stored in memory](https://kripken.github.io/emscripten-site/docs/porting/files/file_systems_overview.html), and thus **doesn't persist the changes** made to the database. However, it allows you to **import** any existing sqlite file, and to **export** the created database as a [JavaScript typed array](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Typed_arrays).
 
 There are no C bindings or node-gyp compilation here, sql.js is a simple JavaScript file, that can be used like any traditional JavaScript library. If you are building a native application in JavaScript (using Electron for instance), or are working in node.js, you will likely prefer to use [a native binding of SQLite to JavaScript](https://www.npmjs.com/package/sqlite3).