build: specify MSRV

Cargo.toml

@@ -9,3 +9,4 @@ keywords = ["memory", "slice", "array"]
 categories = ["data-structures"]
 repository = "https://git.nora.codes/nora/nslice"
 readme = "README.md"
+rust-version = "1.56.1"

README.md

@@ -8,7 +8,7 @@ either exactly or at least some compile-time-known number of values.
 This is useful when dealing with a slice whose length you expect to be exactly
 or at least some particular length;
 rather than making runtime checks on each access,
-you can check the length once and access values freely with no copying. 
+you can check the length once and access values freely with no copying.
 
 ```rust
 # use nslice::MinSlice;
@@ -18,8 +18,13 @@ let minslice: &MinSlice<_, 3> = MinSlice::from_slice(slice).unwrap();
 assert_eq!(minslice.tail.len(), 3);
 assert_eq!(minslice.head[0], 1);
 assert_eq!(minslice.tail[2], 6);
-``` 
+```
+
+## MSRV
+
+This project supports Rust 1.56.1 and onward.
 
 ## License
 
 This project is licensed MIT.
+

rust-toolchain.toml

@@ -0,0 +1,2 @@
+[toolchain]
+channel = "1.56.1"