Complete doc for upgrade to v5 (#33)

Complete doc for upgrade to v5 + Add link to core changelog

Author: gaeljw

docs/upgrade_v5.md

@@ -5,6 +5,8 @@ If you are using Cucumber Scala 4.7.x and want to upgrade to 5.x, please note th
 Starting from version 5.x, Cucumber Scala will try to be as close as possible to the Cucumber Java implementation while remaining Scala oriented.
 This means that package names, parameters order, internal code... will be more consistent with the Java implementation.
 
+See also the [CHANGELOG](https://github.com/cucumber/cucumber-jvm/blob/master/CHANGELOG.md) from Cucumber Core.
+
 ## Packages
 
 All Cucumber Scala classes are now under `io.cucumber.scala` package instead of `cucumber.api.scala`.
@@ -14,7 +16,7 @@ All Cucumber Scala classes are now under `io.cucumber.scala` package instead of
 The `Before`, `BeforeStep`, `After` and `AfterStep` definitions have slightly changed:
 - to apply only to scenarios with some tags, the `String*` parameter is replaced by a single tag expression of type `String`.
 This changes comes from Cucumber itself.
-- if providing both an order and a tag expression, the order is now the second parameter instead of the first.
+- if providing both an _order_ and a _tag expression_, the _order_ is now the second parameter instead of the first.
 This is more consistent with the Java implementation.
 
 For instance, the following code:
@@ -33,4 +35,19 @@ Before("@tag1 or @tag2", 1) { _ =>
 }
 ```
 
-See also the [Hooks documentation](hooks.md).
+### Other changes
+
+As a side effect the following usage no longer compiles:
+```scala
+Before() { _ =>
+  // Do something
+}
+```
+It can be replaced with:
+```scala
+Before { _ =>
+  // Do something
+}
+```
+
+See also the [Hooks documentation](hooks.md).