docs: add readme (#56)

Author: jemlog

README.md

@@ -1,9 +1,141 @@
-# litmus-java-sdk
+# Litmus Java SDK
 
-Compatible only with Litmus version 3.13.0
+[![Slack Channel](https://img.shields.io/badge/Slack-Join-purple)](https://slack.litmuschaos.io)
+[![GitHub issues](https://img.shields.io/github/issues/litmuschaos/litmus-go)](https://github.com/litmuschaos/litmus-go/issues)
+[![Twitter Follow](https://img.shields.io/twitter/follow/litmuschaos?style=social)](https://twitter.com/LitmusChaos)
+[![YouTube Channel](https://img.shields.io/badge/YouTube-Subscribe-red)](https://www.youtube.com/channel/UCa57PMqmz_j0wnteRa9nCaw)
+<br><br>
 
-## TBD
+## **Introduction**
 
-## Contributing to litmus-java-sdk
+The Litmus Java SDK makes it easy to communicate with Litmus’ internal servers.
 
-Check out the [CONTRIBUTING.md](./CONTRIBUTING.md)
+## Requirements
+
+This library requires Java 17 or later.
+
+Litmus version 3.13.0 or later.
+
+## Installation
+
+### Gradle example
+
+```groovy
+implementation 'io.litmuschaos:litmus-sdk:<VERSION>'
+```
+
+### Maven example
+
+```xml
+<dependency>
+    <groupId>io.litmuschaos</groupId>
+    <artifactId>litmus-sdk</artifactId>
+    <version>VERSION</version>
+</dependency>
+```
+
+## LitmusClient
+
+LitmusClient contains simple, easy-to-use interface for making requests to litmus internal servers.
+
+```java
+import io.litmuschaos.LitmusClient;
+import io.litmuschaos.request.UserCreateRequest;
+import io.litmuschaos.response.UserResponse;
+
+String host = "http://localhost:3000"; // LitmusChaos frontend url
+String token = "eyJhbGciOiJIUzUxMiIsInR..." // api token
+
+LitmusClient litmusClient = new LitmusClient(host, token);
+
+UserCreateRequest request = UserCreateRequest.builder()
+         .username("litmus")
+         .password("passwd")
+         .role("user")
+         .email("[email protected]")
+         .build();
+
+UserResponse response = litmusClient.createUser(request);
+```
+
+You can customize httpClient configuration by injecting `LitmusConfig` class.
+
+```java
+LitmusConfig config = new LitmusConfig();
+
+config.setHttpClientReadTimeoutMillis(1000L);
+config.setHttpClientWriteTimeoutMillis(1000L);
+config.setHttpClientConnectTimeoutMillis(1000L);
+        
+LitmusClient litmusClient = new LitmusClient("host", "token", config);
+
+// if you don't need to set custom properties, just pass host and token. 
+// Default configurations are applied.
+LitmusClient litmusClient = new LitmusClient("host", "token");
+```
+
+## How to use ProjectionRoot
+
+You need to understand `projectionRoot` for using Litmus Java SDK well. When you access to litmus graphQL backend server by SDK, you can filter response field by projectionRoot.
+
+```java
+GetEnvironmentGraphQLQuery query = new GetEnvironmentGraphQLQuery.Builder()
+      .projectID("567ccf04-7195-4311-a215-0803fe5e93f6")
+      .environmentID("test-environments")
+      .build();
+        
+GetEnvironmentProjectionRoot projectionRoot = new GetEnvironmentProjectionRoot<>()
+      .projectID()
+      .createdBy().userID().username().root()
+      .name()
+      .updatedBy().userID().username().root();
+
+Environment response = litmusClient.getEnvironment(query, projectionRoot);
+``` 
+litmusClient only return fields that selected by projectionRoot.
+```
+{
+  projectID="567ccf04-7195-4311-a215-0803fe5e93f6",
+  name="test",
+  createdBy={
+    userID="567ccf04-7195-4311",
+    username="test-user",
+    email=null       // not selected
+  }
+  description=null,   // not selected
+  tags=null,          // not selected
+  ...
+}
+```
+
+ProjectionRoot is tree data structure, so you can explore object graph by `parent()` and `root()` method.
+
+- parent() : move to upper position
+- root() : move to root position
+
+```
+{
+  "name": "test",
+  "faultName": "test fault",
+  "executedByExperment": {
+    "experimentID": "test-id",
+    "experimentName": "test-experiment",
+    "updatedBy": {
+      "username": "test-user", // If you call parent() here, you can access to experimentName field
+      "email": "[email protected]" // If you call root() here, you can access to faultName field
+    }
+  }
+}
+```
+
+## **Sample code**
+
+This project contains the following [sample code](https://github.com/litmuschaos/litmus-java-sdk/blob/master/src/test/java/io/litmuschaos/LitmusClientTest.java)
+
+## **Contributing**
+
+We'd love to have you contribute! Please refer to [CONTRIBUTING](./CONTRIBUTING.md) for details.
+
+## License
+
+Here is a copy of the License: [License](./LICENSE)