add screenshot to docs directory

Author: VerosK

docs/INSTALL.md

@@ -0,0 +1,61 @@
+
+# How to start Naglite4 
+
+Naglite4 requires 
+
+## Enable Icinga2 API and setup API user
+
+1. Make sure your Icinga2 can provide API.
+
+      ```bash
+    # check if Icinga 2  API is enabled     
+    icinga2 feature enable api    
+    # if not enabled, run API setup
+    icinga2 api setup
+   ```
+
+2. Create API user by adding following to Icinga2 config 
+
+    ```
+    object ApiUser "naglite"{
+      password = "enter-your-secret-password-here"
+    
+      permissions = [
+                "objects/query/Host",
+                "objects/query/Service",
+                "events/*",    // not really needed
+                "status/query" // not really needed
+                ]
+    }
+    ```
+    
+3. Reload Icinga2 with updated config.
+
+    ```bash
+    # check your Icinga2 config is valid
+    icinga2 daemon validate
+ 
+    # reload Icinga 
+    systemctl reload icinga2
+    ```
+
+## Start Naglite4
+
+1. Setup Naglite together with its dependencies. (or use provided RPM).
+
+2. Start the Flask application service - example systemd unit 
+  starts appliction on `127.0.0.1:4080` 
+
+## Connect web server with application   
+
+2.  Forward requests from webserver to the started Flask application. 
+
+    ```nginx
+        location /naglite4/ {
+                proxy_pass http://localhost:4080/;
+        }
+        location /naglite4/static/ {
+                proxy_pass http://localhost:4080/naglite4/static/ ;
+        }
+     ```
+