Document GenServer shutdown default

Author: josevalim

CHANGELOG.md

@@ -199,7 +199,7 @@ The type system was made possible thanks to a partnership between [CNRS](https:/
 
 #### Elixir
 
-  * `require SomeModule` no longer expands to the given module at compile-time, but it still returns the module at runtime. Note that while Elixir does not guarantee macros will expand to certain constructs, but since this can break code relying on the previous behaviour, such as `require(SomeMod).some_macro()`, we are adding this note to the release notes
+  * `require SomeModule` no longer expands to the given module at compile-time, but it still returns the module at runtime. Note that while Elixir does not guarantee macros will expand to certain constructs, but since this can break code relying on the previous behaviour, such as `require(SomeMod).some_macro()`, we are adding this note to the CHANGELOG
 
 ### 3. Hard deprecations
 

lib/elixir/lib/gen_server.ex

@@ -210,13 +210,14 @@ defmodule GenServer do
     * [`:restart`](`m:Supervisor#module-restart-values-restart`) - when the
       child should be restarted, defaults to `:permanent`
     * [`:shutdown`](`m:Supervisor#module-shutdown-values-shutdown`) - how to
-      shut down the child, either immediately or by giving it time to shut down
+      shut down the child, either immediately or by giving it time to shut down,
+      defaults to `5_000`
 
   For example:
 
       use GenServer, restart: :transient, shutdown: 10_000
 
-  See the ["Child specification"](`m:Supervisor#module-child_spec-1-function`) section in the `Supervisor` module for more
+  See the ["Child specification"](`m:Supervisor#module-child-specification`) section in the `Supervisor` module for more
   detailed information. The `@doc` annotation immediately preceding
   `use GenServer` will be attached to the generated `child_spec/1` function.