Added readme file

README.md

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+## Setup
+
+Using the [plugins DSL][1]:
+
+```groovy
+plugins {
+    id "org.sirekanyan.version-checker" version "1.0.0"
+}
+```
+
+Using [legacy plugin application][2]:
+
+```groovy
+buildscript {
+    repositories {
+        maven {
+            url "https://plugins.gradle.org/m2/"
+        }
+    }
+    dependencies {
+        classpath "org.sirekanyan:version-checker:1.0.0"
+    }
+}
+
+apply plugin: "org.sirekanyan.version-checker"
+```
+
+## Run
+
+```bash
+./gradlew versionChecker
+```
+
+## Options
+
+If you don't want some dependency to be updated to the specific version, consider using `lessThan` inside
+a `versionCheckerOptions` block.
+
+For example:
+
+```kotlin
+versionCheckerOptions {
+    "com.squareup.okhttp3:logging-interceptor" lessThan "4.0"
+}
+```
+
+## Usages
+
+This plugin is actively used during development of [Spacetime](https://github.com/sirekanian/spacetime),
+[Warmongr](https://github.com/sirekanian/warmongr), [Anders Robot](https://github.com/sirekanian/andersrobot),
+and [Knigopis](https://github.com/sirekanian/knigopis)
+
+## Links
+
+- [Gradle Plugin Portal][3]
+
+[1]: https://docs.gradle.org/current/userguide/plugins.html#sec:plugins_block
+[2]: https://docs.gradle.org/current/userguide/plugins.html#sec:old_plugin_application
+[3]: https://plugins.gradle.org/plugin/org.sirekanyan.version-checker