docs(readme): remove MSRV (#1266)

This notice was useful when the `Cargo.toml` had no standardized field
for this. Now it's easier to look it up in the `Cargo.toml` and it's
also a single point of truth. Updating the README was overlooked for
quite some time so it's better to just omit it rather than having
something wrong that will be forgotten again in the future.

README.md

@@ -352,10 +352,6 @@ Pull Request].
 Please make sure you read the updated [contributing](./CONTRIBUTING.md) guidelines, especially if
 you are interested in working on a PR or issue opened in the previous repository.
 
-## Rust version requirements
-
-Since version 0.23.0, The Minimum Supported Rust Version (MSRV) of `ratatui` is 1.67.0.
-
 ## Widgets
 
 ### Built in