Added README

README.md

 # PHP GBIF client
+
+First attempt of a PHP client for the [GBIF API](https://www.gbif.org/developer/summary). See its sibling projects in [R](https://github.com/ropensci/rgbif), [Python](https://github.com/sckott/pygbif) and [Ruby](https://github.com/sckott/gbifrb). Only occurrences (search an retrieval) are currently supported, but features will be added if this project gets enough funding.
+
+A [Drupal module](https://www.drupal.org/project/gbif2) uses this client to enable users to list GBIF occurrences with the Views module on their websites.
+
+## Use
+
+### Get an occurrence knowing its ID (key)
+
+```
+<?php
+
+use ResTelae\Gbif\Occurrences;
+
+$occ = new Occurrences();
+// Returns an array of results.
+$occ->get(2550051996);
+```
+
+### Search
+
+```
+<?php
+
+use ResTelae\Gbif\Occurrences;
+
+$occ = new Occurrences();
+
+// Returns an array of results.
+$occ->search(['taxonKey' => 3329049]);
+
+// Search by dataset key.
+$occ->search([
+  'datasetKey' => '7b5d6a48-f762-11e1-a439-00145eb45e9a',
+  'limit' =>20,
+]);
+
+```
+
+See src/Occurrences.php for more information.