Remove last mentions of Stages (#7553)

# Objective

- Remove mentions of Stages, since they are gone now

## Solution

- Remove mentions of Stages

Author: NiklasEi

crates/bevy_ecs/examples/change_detection.rs

@@ -19,7 +19,7 @@ fn main() {
     // Create a new Schedule, which stores systems and controls their relative ordering
     let mut schedule = Schedule::default();
 
-    // Add systems to the Stage to execute our app logic
+    // Add systems to the Schedule to execute our app logic
     // We can label our systems to force a specific run-order between some of them
     schedule.add_system(spawn_entities.in_set(SimulationSystem::Spawn));
     schedule.add_system(print_counter_when_changed.after(SimulationSystem::Spawn));

docs/plugins_guidelines.md

@@ -71,18 +71,18 @@ In the case of a Bevy plugin, a few screenshots or movies/animated GIFs from you
 
 Additionally, it can be helpful to list:
 
-* Stages added by the plugin
-* Systems used
+* SystemSets available from your plugin
+  * if important, also mention their execution order
 * Components available from your plugin
 
 ### Indicate Compatible Versions
 
 Indicating which version of your plugin works with which version of Bevy can be helpful for your users. Some of your users may be using an older version of Bevy for any number of reasons. You can help them find which version of your plugin they should use. This can be shown as a simple table in your readme with each version of Bevy and the corresponding compatible version of your plugin.
 
-|bevy|bevy_awesome_plugin|
-|---|---|
-|0.5|0.3|
-|0.4|0.1|
+| bevy | bevy_awesome_plugin |
+|------|---------------------|
+| 0.5  | 0.3                 |
+| 0.4  | 0.1                 |
 
 ## Tests and CI