doc: update README

Author: miyataka

README.md

@@ -1 +1,19 @@
 # elasticsearch-github-actions
+
+setup elasticsearch in your github actions' workflow
+
+## Usage
+```yaml
+steps:
+- name: Configure sysctl limits
+  run: |
+    sudo swapoff -a
+    sudo sysctl -w vm.swappiness=1
+    sudo sysctl -w fs.file-max=262144
+    sudo sysctl -w vm.max_map_count=262144
+
+- uses: miyataka/elasticsearch-github-actions
+  with:
+    stack-version: '7.6.2'
+    plugins: 'analysis-kuromoji analysis-icu'
+```