add manual_option_as_slice MSRV to the lint documentation (#14171)

`manual_option_as_slice` takes MSRV into account, but this is not
mentioned in the lint documentation.

changelog: none

Author: Centri3

book/src/lint_configuration.md

@@ -748,6 +748,7 @@ The minimum rust version that the project supports. Defaults to the `rust-versio
 * [`manual_is_ascii_check`](https://rust-lang.github.io/rust-clippy/master/index.html#manual_is_ascii_check)
 * [`manual_let_else`](https://rust-lang.github.io/rust-clippy/master/index.html#manual_let_else)
 * [`manual_non_exhaustive`](https://rust-lang.github.io/rust-clippy/master/index.html#manual_non_exhaustive)
+* [`manual_option_as_slice`](https://rust-lang.github.io/rust-clippy/master/index.html#manual_option_as_slice)
 * [`manual_pattern_char_comparison`](https://rust-lang.github.io/rust-clippy/master/index.html#manual_pattern_char_comparison)
 * [`manual_range_contains`](https://rust-lang.github.io/rust-clippy/master/index.html#manual_range_contains)
 * [`manual_rem_euclid`](https://rust-lang.github.io/rust-clippy/master/index.html#manual_rem_euclid)

clippy_config/src/conf.rs

@@ -617,6 +617,7 @@ define_Conf! {
         manual_is_ascii_check,
         manual_let_else,
         manual_non_exhaustive,
+        manual_option_as_slice,
         manual_pattern_char_comparison,
         manual_range_contains,
         manual_rem_euclid,