Add logo to docs

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

README.md

@@ -1,3 +1,6 @@
+<img src="assets/logo/horizontal/color/krew-horizontal-color.png" width="480"
+  alt="Krew logo"/>
+
 # krew
 
 [![Build Status](https://travis-ci.org/kubernetes-sigs/krew.svg?branch=master)](https://travis-ci.org/kubernetes-sigs/krew)

docs/KREW_LOGO.md

@@ -0,0 +1,53 @@
+# Krew logo
+
+Krew logo is designed by [@iboonox](https://github.com/iboonox) and it is
+licensed under Apache 2.0 license.
+
+## Available logo types
+
+<!-- below we use a table so we can control max height -->
+<table>
+    <thead>
+        <tr>
+            <td>Type</td>
+            <td>Preview</td>
+        </tr>
+    </thead>
+    <tbody>
+        <tr>
+            <td>Horizontal</td>
+            <td>
+                <img src="../assets/logo/horizontal/color/krew-horizontal-color.png"
+                    height="90"/>
+            </td>
+        </tr>
+        <tr>
+            <td>Stacked</td>
+            <td>
+                <img src="../assets/logo/stacked/color/krew-stacked-color.png"
+                    height="90"/>
+            </td>
+        </tr>
+        <tr>
+            <td>Icon-only</td>
+            <td>
+                <img src="../assets/logo/icon/color/krew-icon-color.png"
+                    height="90a"/>
+            </td>
+        </tr>
+    <tbody>
+</table>
+
+## Logo assets
+
+| Type | Color Scheme | Format |
+|--|--|--|
+| horizontal (text next to the icon) | colored | [png](../assets/logo/horizontal/color/krew-horizontal-color.png)  [svg](../assets/logo/horizontal/color/krew-horizontal-color.svg) |
+| horizontal (text next to the icon) | black | [png](../assets/logo/horizontal/black/krew-horizontal-black.png)  [svg](../assets/logo/horizontal/black/krew-horizontal-black.svg) |
+| horizontal (text next to the icon) | white | [png](../assets/logo/horizontal/white/krew-horizontal-white.png)  [svg](../assets/logo/horizontal/white/krew-horizontal-black.svg) |
+| stacked (text below the icon) | colored | [png](../assets/logo/stacked/color/krew-stacked-color.png)  [svg](../assets/logo/stacked/color/krew-stacked-color.svg) |
+| stacked (text below the icon) | black | [png](../assets/logo/stacked/black/krew-stacked-black.png)  [svg](../assets/logo/stacked/black/krew-stacked-black.svg) |
+| stacked (text below the icon) | white | [png](../assets/logo/stacked/white/krew-stacked-white.png)  [svg](../assets/logo/stacked/white/krew-stacked-black.svg) |
+| icon-only | colored | [png](../assets/logo/icon/color/krew-icon-color.png)  [svg](../assets/logo/icon/color/krew-icon-color.svg) |
+| icon-only | black | [png](../assets/logo/icon/black/krew-icon-black.png)  [svg](../assets/logo/icon/black/krew-icon-black.svg) |
+| icon-only | white | [png](../assets/logo/icon/white/krew-icon-white.png)  [svg](../assets/logo/icon/white/krew-icon-black.svg) |