Updated installation docs for version 3.0

docs/sources/installation/configuration.md

@@ -0,0 +1,75 @@
+# Configuration
+
+To add new Zabbix data source open _Data Sources_ in side panel, click _Add new_ and select Zabbix
+from dropdown list.
+
+![Add zabbix data source](../img/installation-add_datasource.png)
+
+Then configure a data source
+
+![Configure zabbix data source](../img/installation-datasource_config.png)
+
+### Http settings
+
+- **Url**: set Zabbix API url (full path with `api_jsonrpc.php`).
+- **Access**: can be either _proxy_ or _direct_.
+- **Http Auth**: configure if you use proxy authentication.
+    - **Basic Auth**:
+    - **With Credentials**:
+
+### Zabbiz API details
+
+- **User** and **Password**: setup login for access to Zabbix API. Also check user's permissions
+in Zabbix if you can't get any groups and hosts in Grafana.
+- **Trends**: enable if you use patch for trends
+support in Zabbix 2.x ([ZBXNEXT-1193](https://support.zabbix.com/browse/ZBXNEXT-1193)). This is
+strictly recommended for displaying long time periods (more than few days, depending of your item's
+updating interval in Zabbix) because few days of item history contains tons of points. Using trends
+can increase Grafana performance.
+    - **Use trends from**: time after which trends will be used. Default is **7d** (7 days).
+    You can set the time in Grafana format. Valid time specificators are:
+        - **h** - hours
+        - **d** - days
+        - **M** - months
+- **Metrics limit**: maximum items number which can be returned by one request. Helps to prevent
+Grafana slowdown due wrong request.
+
+Then click _Add_ - datasource will be added and you can check connection using _Test Connection_ button.
+
+![Test Connection](../img/installation-test_connection.png)
+
+This feature can help to find some mistakes like invalid user name or password, wrong api url.
+
+![Test Connection - Error](../img/installation-test_connection_error.png)
+
+
+## Note about Zabbix 2.2 or less
+Zabbix API (api_jsonrpc.php) before zabbix 2.4 don't allow cross-domain requests (CORS). And you
+can get HTTP error 412 (Precondition Failed).
+To fix it add this code to api_jsonrpc.php immediately after the copyright:
+
+```php
+header('Access-Control-Allow-Origin: *');
+header('Access-Control-Allow-Headers: Content-Type');
+header('Access-Control-Allow-Methods: POST');
+header('Access-Control-Max-Age: 1000');
+
+if ($_SERVER['REQUEST_METHOD'] === 'OPTIONS') {
+  return;
+}
+```
+before
+
+```php
+require_once dirname(__FILE__).'/include/func.inc.php';
+require_once dirname(__FILE__).'/include/classes/core/CHttpRequest.php';
+```
+[Full fix listing](https://gist.github.com/alexanderzobnin/f2348f318d7a93466a0c).
+For more details see zabbix issues [ZBXNEXT-1377](https://support.zabbix.com/browse/ZBXNEXT-1377)
+and [ZBX-8459](https://support.zabbix.com/browse/ZBX-8459).
+
+## Note about Browser Cache
+After updating plugin, clear browser cache and reload application page. See details
+for [Chrome](https://support.google.com/chrome/answer/95582),
+[Firefox](https://support.mozilla.org/en-US/kb/how-clear-firefox-cache). You need to clear cache
+only, not cookies, history and other data.