Upgrade MSRV to 1.70

Many of our dependencies already made the jump and require a cargo update hack, so make it official

Removed the MSRV from the README since it applies to master branch and people read the readme also for
the released version. There is enough documentation of the MSRV in other locations.

docs/tutorial/node/src/getting_started.md

@@ -6,7 +6,7 @@ In this tutorial, we use JavaScript as the host programming language. We also su
 
 You'll need a development environment with [Node.js 16](https://nodejs.org/download/release/v16.19.1/) and [npm](https://www.npmjs.com/) installed. More recent
 versions of NodeJS are currently not supported, for details check [Issue #961](https://github.com/slint-ui/slint/issues/961).
-Since Slint is implemented in the Rust programming language, you also need to install a Rust compiler (1.66 or newer). You can easily install a Rust compiler
+Since Slint is implemented in the Rust programming language, you also need to install a Rust compiler (1.70 or newer). You can easily install a Rust compiler
 following the instruction from [the Rust website](https://www.rust-lang.org/learn/get-started).
 You will also need some additional platform-specific dependencies, see <https://github.com/slint-ui/slint/blob/master/docs/building.md#prerequisites>
 
@@ -45,4 +45,4 @@ and a window will appear with the green "Hello World" greeting.
 
 ![Screenshot of initial tutorial app showing Hello World](https://slint.dev/blog/memory-game-tutorial/getting-started.png "Hello World")
 
-Feel free to use your favorite IDE for this purpose.
+Feel free to use your favorite IDE for this purpose.