Adds CHANGELOG and UPGRADE entries.

Author: LeFnord

CHANGELOG.md

@@ -6,6 +6,8 @@
 
 #### Fixes
 
+* Your contribution here.
+* [#340](https://github.com/ruby-grape/grape-entity/pull/340): Preparations for 3.0 - [@LeFnord](https://github.com/LeFnord).
 * [#338](https://github.com/ruby-grape/grape-entity/pull/338): Fix ruby 2.7 deprecation warning - [@begotten63](https://github.com/begotten63).
 
 ### 0.8.1 (2020-07-15)

UPGRADING.md

@@ -1,6 +1,21 @@
 Upgrading Grape Entity
 ===============
 
+### Upgrading to >= 0.8.2
+
+In Ruby 3.0: the block handling will be changed
+[language-changes point 3, Proc](https://github.com/ruby/ruby/blob/v3_0_0_preview1/NEWS.md#language-changes).
+This:
+```ruby
+expose :that_method_without_args, &:method_without_args
+```
+will be deprecated.
+
+Prefer to use this pattern for simple setting a value
+```ruby
+expose :method_without_args, as: :that_method_without_args
+```
+
 ### Upgrading to >= 0.6.0
 
 #### Changes in Grape::Entity#inspect