Mention that unsupported targets no longer compile

Signed-off-by: Joe Richey <[email protected]>

Author: josephlr

CHANGELOG.md

@@ -14,6 +14,7 @@ The following (off by default) Cargo features have been added:
 - `"custom"` - allows a user to specify a custom implementation [#109]
 
 ### Breaking Changes
+- Unsupported targets no longer compile [#107]
 - Change/Add `Error` constants [#120]
 - Only impl `std` traits when the `"std"` Cargo feature is specified [#106]
 - Remove offical support for Hermit, L4Re, and UEFI [#133]
@@ -22,6 +23,7 @@ The following (off by default) Cargo features have been added:
 - Update MSRV to 1.34 [#159]
 
 [#106]: https://github.com/rust-random/getrandom/pull/106
+[#107]: https://github.com/rust-random/getrandom/pull/107
 [#109]: https://github.com/rust-random/getrandom/pull/109
 [#120]: https://github.com/rust-random/getrandom/pull/120
 [#131]: https://github.com/rust-random/getrandom/pull/131