Specify rust-version and remove outdated info from README

The workspace does not compile with Rust 1.60.0 due to a neon target feature:

```log
error[E0658]: the target feature `neon` is currently unstable
  --> src/simd/aarch64.rs:11:18
   |
11 | #[target_feature(enable = "neon")]
   |                  ^^^^^^^^^^^^^^^
   |
   = note: see issue #44839 <rust-lang/rust#44839> for more information
```

Author: xtqqczze

Cargo.toml

@@ -2,6 +2,7 @@
 authors = ["Andre Bogus <bogusandre@gmail.de>", "Joshua Landau <joshua@landau.ws>"]
 description = "count occurrences of a given byte, or the number of UTF-8 code points, in a byte slice, fast"
 edition = "2018"
+rust-version = "1.61.0"
 name = "bytecount"
 version = "0.6.9"
 license = "Apache-2.0/MIT"

README.md

@@ -64,9 +64,6 @@ RUSTFLAGS="-C target-cpu=native" cargo build --release
 
 The scalar algorithm is explained in depth [here](https://llogiq.github.io/2016/09/27/count.html).
 
-**Note: Versions until 0.4.0 worked with Rust as of 1.20.0. Version 0.5.0 until 0.6.0 requires Rust 1.26 or later,
-and at least 1.27.2 to use SIMD. Versions from 0.6.0 require Rust 1.32.0 or later.**
-
 ## License
 
 Licensed under either of at your discretion: