docs: greatly improve readme w/ simplified examples and motivation

package.json

@@ -1,7 +1,7 @@
 {
   "name": "es-painless-fields",
   "version": "0.1.0",
-  "description": "Generate Painless Elasticsearch script to set / unset fields on document from JavaScript Object",
+  "description": "Helpers for bulk update Elasticsearch documents by query using Painless scripts",
   "license": "MIT",
   "repository": "vladgolubev/es-painless-fields",
   "author": {
@@ -19,7 +19,14 @@
   "files": [
     "index.js"
   ],
-  "keywords": [],
+  "keywords": [
+    "elasticsearch",
+    "bulk update",
+    "update by query",
+    "painless",
+    "scripts",
+    "replace fields"
+  ],
   "dependencies": {},
   "devDependencies": {
     "jest": "^21.2.1"

readme.md

@@ -1,57 +1,52 @@
 # es-painless-fields [![Build Status](https://travis-ci.org/vladgolubev/es-painless-fields.svg?branch=master)](https://travis-ci.org/vladgolubev/es-painless-fields)
 
-> Generate Painless Elasticsearch script to set / unset fields on document from JavaScript Object
+> Helpers for bulk update Elasticsearch documents by query using Painless scripts
 
 ## Install
 
 ```
 $ yarn add es-painless-fields
 ```
 
-## Usage
+## Features & Motivation
+
+The main purpose is to utilize `_update_by_query` Elasticsearch API most efficiently.
+API is limited to updating documents in-place by scripts, so you cannot rely on ES to replace document by passing partial parameters. This package aims to ease partial bulk document updates.
 
-WIP: Currently only simple `set` and `replace` commands present.
+* In-place **set** values to fields
+* In-place **replace** values in fields
+* **Zero** dependencies!
+* ... to be done
+
+## Usage
 
 ```js
 const esClient = require('elasticsearch').Client();
-const esPainlessFields = require('es-painless-fields');
-
-const docUpdateScript = esPainlessFields.set({a: 1, b: 2});
-
-/*
-  {
-    "lang": "painless",
-    "source": "ctx._source.a = params.a; ctx._source.b = params.b;",
-    "params": {
-      "a": 1,
-      "b": 2
-    }
-  }
- */
+const painlessFields = require('es-painless-fields');
 
+const script = painlessFields.set({a: 1, b: 2});
 
-// Now we can perform a bulk update
 esClient.updateByQuery({
   conflicts: 'proceed',
   body: {
-    query: {term: {user: 'kimchy'}},
-    script: docUpdateScript
+    query: {match_all: {}},
+    script
   }
 });
 
 ```
 
 ## API
 
-### esPainlessFields.set(fieldsMap)
+### .set(fieldsMap)
 
 #### fieldsMap
 
 Type: `Object`
 
-Object fields which you would like to set.
+Object fields which you would like to set. Example: `{a: 1, b: 2}`
 
-### esPainlessFields.replace(fieldsReplacements)
+### .replace(fieldsReplacements)
 
 #### fieldsReplacements