Document platform support policy (#387)

README.md

@@ -54,6 +54,14 @@ crate features, WASM support and Custom RNGs see the
 
 This crate requires Rust 1.36.0 or later.
 
+## Platform Support
+
+This crate generally supports the same operating system and platform versions that the Rust standard library does. 
+Additional targets may be supported using pluggable custom implementations.
+
+This means that as Rust drops support for old versions of operating systems (such as old Linux kernel versions, Android API levels, etc)
+in stable releases, `getrandom` may create new patch releases (`0.N.x`) that remove support for outdated platform versions.
+
 # License
 
 The `getrandom` library is distributed under either of

src/lib.rs

@@ -106,6 +106,13 @@
 //! ```
 //! This crate will then use the provided `webcrypto` implementation.
 //!
+//! ### Platform Support
+//! This crate generally supports the same operating system and platform versions that the Rust standard library does.
+//! Additional targets may be supported using pluggable custom implementations.
+//!
+//! This means that as Rust drops support for old versions of operating systems (such as old Linux kernel versions, Android API levels, etc)
+//! in stable releases, `getrandom` may create new patch releases (`0.N.x`) that remove support for outdated platform versions.
+//!
 //! ### Custom implementations
 //!
 //! The [`register_custom_getrandom!`] macro allows a user to mark their own