docs(readme): declare MSRV policy

README.md

@@ -10,6 +10,18 @@
 
 An ergonomic physics API for 2d and 3d [bevy] games. (powered by [rapier])
 
+
+## Design principles
+
+* Use [bevy] types, resources and components when possible (`Vec3`, `Quat`, `Transform`, `Events`, etc.)
+* Provide a single API that works for both 2d and 3d.
+* Data oriented. Using this library should feel like its a part of [bevy].
+* Avoid asking the user to lookup in resources via *handles*. Data should be accessible and modifiable directly in components.
+* Hide the actual physics engine. This is an implementation detail the user shouldn't have to worry about.
+    * But, allow advanced users to access the underlying [rapier] resources, so the user is never blocked by a missing
+      element in the API of heron.
+
+
 ## What it looks like
 
 ```rust,no_run
@@ -73,30 +85,10 @@ heron = { version = "2.3.0", features = ["3d"] }
 <!--- x-release-please-end-version --->
 
 
-## Supported Bevy Versions
-
-| bevy | heron      |
-|------|------------|
-| 0.6  | 1 - 2      |
-| 0.5  | 0.4 - 0.13 |
-| 0.4  | 0.1 - 0.3  |
-
-## Design principles
-
-* Use [bevy] types, resources and components when possible (`Vec3`, `Quat`, `Transform`, `Events`, etc.)
-* Provide a single API that works for both 2d and 3d. (Like bevy does)
-* Data oriented. Using this library should feel like its a part of [bevy].
-* Avoid asking the user to lookup in resources via *handles*. Data should be accessible and modifiable directly in components.
-* Hide the actual physics engine. This is an implementation detail the user shouldn't have to worry about.
-    * But, allow advanced users to access the underlying [rapier] resources, so the user is never blocked by a missing
-      element in the API of heron.
-
-
 ## Feature flags
 
 One must choose to use either `2d` or `3d`. If neither of the two features is enabled, the `PhysicsPlugin` won't be available.
 
-
 * `collision-from-mesh` Add a component to generate convex hull collision for a mesh.
 * `3d` Enable simulation on the 3 axes `x`, `y`, and `z`.
 * `2d` Enable simulation only on the first 2 axes `x` and `y`.
@@ -105,6 +97,24 @@ One must choose to use either `2d` or `3d`. If neither of the two features is en
 * `enhanced-determinism` Enable rapier's [enhanced-determinism](https://rapier.rs/docs/user_guides/rust/determinism)
 
 
+## MSRV
+
+The minimum supported rust version is currently: `1.57`
+
+**It *may* be increased to a newer stable version in a minor release.** (but only if needed)
+
+It *will* be increased to the latest stable version in a major release. (even if not needed)
+
+
+## Supported Bevy Versions
+
+| bevy | heron      |
+|------|------------|
+| 0.6  | 1 - 2      |
+| 0.5  | 0.4 - 0.13 |
+| 0.4  | 0.1 - 0.3  |
+
+
 ## How does this project compare to bevy_rapier?
 
 [bevy_rapier] plugin is an excellent option and should definitely be considered.