added migration guide file

MIGRATION.md

@@ -0,0 +1,19 @@
+## Upgrading from 1.0.1 to 2.0.0
+Upgrading to 2.0.0 introduces breaking API changes. 
+
+JavaScript `Date` and `Number` prototypes are no longer patched by this library. 
+The library should now be pure without any side effects.
+
+This means you can no longer depend on methods like `formattedTime` being directly accessible on the Date instance. For example,
+
+**Before**:
+
+```js
+prayerTimes.fajr.formattedTime(); // no longer works
+```
+
+**After**:
+
+```js
+adhan.Date.formattedTime(prayerTimes.fajr); // works
+```

README.md

@@ -30,11 +30,11 @@ and then require the module
 var adhan = require('adhan')
 ```
 
-Read [migration guide from version 1.x](MIGRATION.md)
-
 
 ## Usage
 
+Migrating from version 1.x? Read the [migration guide](MIGRATION.md)
+
 To get prayer times initialize a new `PrayerTimes` object passing in coordinates,
 date, and calculation parameters.