Merge pull request #2 from jtsunne/add-readme

add Readme

README.md

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+# Nagios-ES
+
+## Description
+
+This is a Nagios plugin that checks the status of Elasticsearch cluster.
+
+## Build
+
+```
+go build -o check_es .
+```
+
+## Usage
+
+```
+check_es --es_url=http://<domain>:<port> --check=<check_name> --w=50 --c=90
+```
+
+### Options
+
+- `es_url`: Elasticsearch URL (format: http://<domain>:<port>)
+- `check`: Check name
+  - `health`: Check cluster health
+  - `node_count`: Overall nodes count (W/C required)
+  - `data_node_count`: Check data nodes count (W/C required)
+  - `cpu_usage`: Check node CPU usage (W/C required)
+    - If filter will be used, it will check the CPU usage of the specific node
+    - If filter is not used, it will check the maximum CPU usage of all nodes
+  - `heap_size`: Check node Head usage (W/C required)
+    - If filter will be used, it will check the Heap usage of the specific node
+    - If filter is not used, it will check the maximum Heap usage of all nodes
+  - `disk_usage`: Check node Disk usage (W/C required)
+    - If filter will be used, it will check the Disk usage of the specific node
+    - If filter is not used, it will check the maximum Disk usage of all nodes
+- `w`: Warning threshold
+- `c`: Critical threshold
+For filtering node specific checks, you can use the following options:
+- `node_ip`: Node IP address for node specific checks
+- `node_name`: Node name for node specific checks
+
+## Example
+
+```
+./check_es --es_url=http://<domain>:<port> --check=health
+```
+
+OK Output:
+```
+OK: Cluster health is green | 'time'=19ms;;;;
+```
+
+Warning Output:
+```
+WARNING: Cluster health is yellow, relocating shards: 0 | 'active_shards'=5;;;; 'relocating_shards'=0;;;; 'time'=24ms;;;; 'unassigned_shards'=3;;;;
+```