docs(migration): add initial migration instructions

Author: axe312ger

MIGRATION.md

@@ -0,0 +1,56 @@
+# Migration
+
+## Migrating from v0 to v1
+
+Most important notes:
+
+* The API is now async
+* The new plugin based system requires a different configuration
+* The result is now as a Buffer available as `result.content`
+* All other metadata is now available within `result.metadata`
+
+
+**old API**:
+```js
+;(async () => {
+  const absolutePath = '/foo/bar/baz.jpg'
+
+  const result = await new Promise((resolve, reject) => {
+    try {
+      const result = sqip({
+        filename: absolutePath,
+        // other options
+      })
+      resolve(result)
+    } catch (error) {
+      reject(error)
+    }
+  })
+
+  // Content
+  console.log(result.final_svg)
+
+  // Metadata
+  console.log(result.width)
+  console.log(result.height)
+  console.log(result.type)
+})()
+```
+
+**new API**:
+```js
+;(async () => {
+  const absolutePath = '/foo/bar/baz.jpg'
+
+  const result = await sqip({
+    input: absolutePath,
+    // other options like output or plugin config
+  })
+
+  // Content (as buffer!)
+  console.log(result.content)
+
+  // Metadata
+  console.log(result.metadata)
+})()
+```