README tweaks

README.md

@@ -9,7 +9,7 @@ Rand is a set of crates supporting (pseudo-)random generators:
 
 -   Built over a standard RNG trait: [`rand_core::RngCore`](https://docs.rs/rand_core/latest/rand_core/trait.RngCore.html)
 -   With fast implementations of both [strong](https://rust-random.github.io/book/guide-rngs.html#cryptographically-secure-pseudo-random-number-generators-csprngs) and
-    [small](https://rust-random.github.io/book/guide-rngs.html#basic-pseudo-random-number-generators-prngs) generators: [`rand::rngs`](https://docs.rs/rand/latest/rand/rngs/index.html), and more RNGs: [`rand_chacha`](https://docs.rs/rand_chacha), [`rand_xoshiro`](https://docs.rs/rand_xoshiro/), [`rand_pcg`](https://docs.rs/rand_pcg/), [rngs repo](https://github.com/rust-random/rngs/)
+    [small](https://rust-random.github.io/book/guide-rngs.html#basic-pseudo-random-number-generators-prngs) generators: [`rand::rngs`](https://docs.rs/rand/latest/rand/rngs/index.html), and more RNGs: [`chacha20`](https://docs.rs/chacha20), [`rand_xoshiro`](https://docs.rs/rand_xoshiro/), [`rand_pcg`](https://docs.rs/rand_pcg/), [`rand_sfc`](https://docs.rs/rand_sfc/), [`rand_seeder`](https://docs.rs/rand_seeder/), [rngs repo](https://github.com/rust-random/rngs/)
 -   [`rand::rng`](https://docs.rs/rand/latest/rand/fn.rng.html) is an asymptotically-fast, automatically-seeded and reasonably strong generator available on all `std` targets
 -   Direct support for seeding generators from the [getrandom] crate
 
@@ -64,13 +64,16 @@ See the [CHANGELOG](https://github.com/rust-random/rand/blob/master/CHANGELOG.md
 Rand is built with these features enabled by default:
 
 -   `std` enables functionality dependent on the `std` lib
--   `alloc` (implied by `std`) enables functionality requiring an allocator
--   `sys_rng` (implied by `std`) enables `rngs::SysRng`, using the [getrandom] crate
--   `std_rng` enables inclusion of `StdRng`, `ThreadRng`
+-   `alloc` (implied by `std`) enables functionality requiring an allocator; a
+    significant portion of sequence and distribution functionality requires this
+-   `sys_rng` enables `rand::rngs::SysRng` (uses the [getrandom] crate)
+-   `std_rng` enables `rand::rngs::StdRng` (uses the [chacha20] crate)
+-   `thread_rng` (implies `std`, `std_rng`, `sys_rng`) enables `rand::rngs::ThreadRng` and `rand::rng()`
 
 Optionally, the following dependencies can be enabled:
 
--   `log` enables logging via [log](https://crates.io/crates/log)
+-   `chacha` enables `rand::rngs::{ChaCha8Rng, ChaCha12Rng, ChaCha20Rng}` (uses the [chacha20] crate)
+-   `log` enables logging (uses the [log] crate)
 
 Additionally, these features configure Rand:
 
@@ -83,11 +86,6 @@ Additionally, these features configure Rand:
 
     Note: enabling this option is expected to affect reproducibility of results.
 
-Rand supports limited functionality in `no_std` mode (enabled via
-`default-features = false`). In this case, `SysRng` is
-unavailable (unless `sys_rng` is enabled), large parts of `seq` are
-unavailable (unless `alloc` is enabled), and `ThreadRng` is unavailable.
-
 ## Portability
 
 ### Reproducibility
@@ -111,3 +109,5 @@ See [LICENSE-APACHE](https://github.com/rust-random/rand/blob/master/LICENSE-APA
 [COPYRIGHT](https://github.com/rust-random/rand/blob/master/COPYRIGHT) for details.
 
 [getrandom]: https://crates.io/crates/getrandom
+[chacha20]: https://crates.io/crates/chacha20
+[log]: https://crates.io/crates/log