ADD Readme

Author: Thundernerd

Editor/Constrain.cs

@@ -3,7 +3,7 @@
 
 namespace TNRD.Constraints
 {
-    public class Constrain
+    public static class Constrain
     {
         public static ConstrainedRect To(EditorWindow editorWindow)
         {

README.md

@@ -0,0 +1,82 @@
+# Constrained Rect
+
+<p align="center">
+	<a href="#">
+		<img alt="GitHub package.json version" src ="https://img.shields.io/github/package-json/v/Thundernerd/Unity3D-ConstrainedRect" />
+	</a>
+		<a href="#">
+		<img alt="GitHub issues" src ="https://img.shields.io/github/issues/Thundernerd/Unity3D-ConstrainedRect" />
+	</a>
+		<a href="#">
+		<img alt="GitHub pull requests" src ="https://img.shields.io/github/issues-pr/Thundernerd/Unity3D-ConstrainedRect" />
+	</a>
+		<a href="#">
+		<img alt="GitHub license" src ="https://img.shields.io/github/license/Thundernerd/Unity3D-ConstrainedRect" />
+	</a>
+		<a href="#">
+		<img alt="GitHub last commit" src ="https://img.shields.io/github/last-commit/Thundernerd/Unity3D-ConstrainedRect" />
+	</a>
+</p>
+
+Constrained Rect is a small helper that aims to make it easier to create Rect's based on existing ones.
+
+## Usage
+Using constrained rects is easy. You simply call `Constrain.To(...)` and pass it either a `Rect` or an `EditorWindow`.
+
+
+Here's an example using a simple Rect
+```csharp
+private void Foo()
+{
+    Rect rect = new Rect(16, 16, 128, 128);
+
+    Rect constrainedRect = Constrain.To(rect)
+        .Left.Relative(8)
+        .Top.Relative(16)
+        .Right.Relative(24)
+        .Bottom.Relative(32)
+        .ToRect();
+
+    Debug.Log(constrainedRect.xMin); // Logs 24
+    Debug.Log(constrainedRect.yMin); // Logs 32
+    Debug.Log(constrainedRect.xMax); // Logs 104
+    Debug.Log(constrainedRect.yMax); // Logs 96
+}
+```
+
+Aside from `Left`, `Top`, `Right`, and `Bottom`, you can also use `Width` and `Height`. These will **override** `Right` and `Bottom` respectively.
+
+Other modifiers are `Absolute` and `Percentage`. 
+Absolute is what it suggests: instead of taking into account it's constraints it just returns the value given.
+
+Percentage expects a float value between 0 and 1 (inclusive) and multiplies that value with the constrained property.
+```csharp
+private void Foo()
+{
+    Rect rect = new Rect(16, 16, 128, 128);
+
+    Rect constrainedRect = Constrain.To(rect)
+        .Width.Percentage(0.5f)
+        .ToRect();
+
+    Debug.Log(constrainedRect.width); // Logs 64
+}
+```
+
+## Contributing
+Pull requests are welcomed. Please feel free to fix any issues you find, or add new features.
+
+## Installing
+Installing Constrained Rect into your Unity3D project is done through the [Package Manager](https://docs.unity3d.com/Manual/Packages.html).
+
+You can either add the package manually to the [manifest.json](https://docs.unity3d.com/Manual/upm-dependencies.html) file:
+```json
+{
+    "dependencies": {
+        "net.tnrd.constrainedrect": "https://github.com/thundernerd/unity3d-constrainedrect"
+    }
+}
+```
+
+Or add it through the UI by selecting the **+ button** in the top left of the Package Manager, selecting _Add package from git URL..._, and pasting https://github.com/Thundernerd/Unity3D-ConstrainedRect.git in the input field.
+