[Docs] API registerAdapter Method

<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8">
  <title>ZingGrid: Blank Grid</title>
  <script nonce="undefined" src="https://cdn.zinggrid.com/zinggrid.min.js"></script>
  <style>
    body {
      background: #e6e6e6;
    }

    zing-grid[loading] {
      height: 668px;
    }
  </style>
</head>

<body>
  <zing-grid editor caption="Movies" search pager page-size="10">
    <zg-data src="https://zinggrid-examples.firebaseio.com/movies/" adapter="customFirebaseAdapter"></zg-data>
  </zing-grid>
  <script>
    ZingGrid.setLicense(['26ccbfec16b8be9ee98c7d57bee6e498']);
    window.addEventListener('load', function() {
      // define customFirebaseAdapter
      const customFirebaseAdapter = {
        startAtKey: 'startAt',
        limitToKey: 'limitToFirst',
        sortByKey: 'orderBy',
        searchKey: 'equalTo',
        startAtValue: true,
        addValueQuotes: true,
        // firebase requires quotes around sort values
        sortBy: '"title"',
      };

      ZingGrid.registerAdapter('customFirebaseAdapter', customFirebaseAdapter);


    });
  </script>
</body>

</html>

<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8">
  <title>ZingGrid: Blank Grid</title>
  <script src="https://cdn.zinggrid.com/zinggrid.min.js"></script>
</head>

<body>
  <zing-grid editor caption="Movies" search pager page-size="10">
    <zg-data src="https://zinggrid-examples.firebaseio.com/movies/" adapter="customFirebaseAdapter"></zg-data>
  </zing-grid>
</body>

</html>

body {
  background: #e6e6e6;
}

window.addEventListener('load', function() {
  // define customFirebaseAdapter
  const customFirebaseAdapter = {
    startAtKey: 'startAt',
    limitToKey: 'limitToFirst',
    sortByKey: 'orderBy',
    searchKey: 'equalTo',
    startAtValue: true,
    addValueQuotes: true,
    // firebase requires quotes around sort values
    sortBy: '"title"',
  };

  ZingGrid.registerAdapter('customFirebaseAdapter', customFirebaseAdapter);


});