docs(slash): add migration guide for button component from V1

MIGRATION-GUIDE-SLASH-FROM-V1.md

@@ -0,0 +1,36 @@
+# Migration Guide Slash from V1
+
+## Button Component
+
+### Use custom class
+
+```diff
+- <Button className="af-btn my-custom-class">Button</Button>
++ <Button className="my-custom-class">Button</Button>
+```
+
+### Use class modifier
+
+Prop `classModifier` has removed, use props `variant`, `size` instead.
+
+```diff
+- <Button classModifier="reverse small">Button</Button>
++ <Button variant="secondary" size="small">Button</Button>
+```
+
+### Use Icon
+
+```diff
+- <Button classModifier="hasIconLeft">
+-   <i className={`glyphicon glyphicon-arrow-left`} />
+-   Button
+- </Button>
++ <Button leftIcon={<i className={`glyphicon glyphicon-arrow-left`} />}>Button</Button>
+```
+
+### Disabled Button
+
+```diff
+- <Button classModifier="disabled">Button</Button>
++ <Button disabled>Button</Button>
+```