Add readme

README.md

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+# Reason
+
+Sometimes, you need to know not only can be things done or not,
+but also _why_ things can be done.
+
+## Reason status
+
+Status describes current state of reason. It must be convertible to integer value -
+status weight. Status with higher weight worse then smaller weight. 
+(Make sense for appending and joining.)
+
+## Appending reasons (orX)
+
+Reasons can be appended to other reasons. It operations can be matched with `logical or`.
+Reason with the lowest weight wins. If two reasons have same weight, those messages
+will be merged.
+
+```php
+// weight: 1
+// messages: foo, bar
+$first = new Reason(...);
+
+// weight: 2
+// messages: baz
+$second = new Reason(...);
+
+// weight: 1
+// messages: foo, bar
+$firstOrSecond = $first->orX($second);
+
+// weight: 1
+// messages: foobar
+$third = new Reason(...);
+
+// weight: 1
+// messages: foo, bar, foobar
+$firstOrThird = $first->orX($third);
+```
+
+## Joining reasons (andX)
+
+Same behavior as appending, but reason with the highest weight wins.
+Looks like `logical and` operation.
+
+```php
+// weight: 1
+// messages: foo, bar
+$first = new Reason(...);
+
+// weight: 2
+// messages: baz
+$second = new Reason(...);
+
+// weight: 2
+// messages: baz
+$firstAndSecond = $first->andX($second);
+
+// weight: 1
+// messages: foobar
+$third = new Reason(...);
+
+// weight: 1
+// messages: foo, bar, foobar
+$firstAndThird = $first->andX($third);
+```
+
+## Testing
+
+```
+$ vendor/bin/phpunit
+```