docs: improvements in book - closes #1845 (#1856)

docs/book/src/02_getting_started.md

@@ -36,13 +36,23 @@ cargo add leptos --features=csr
 
 > Using `nightly` Rust, and the `nightly` feature in Leptos enables the function-call syntax for signal getters and setters that is used in most of this book.
 >
-> To use `nightly` Rust, you can run
+> To use nightly Rust, you can either opt into nightly for all your Rust projects by running
 >
 > ```bash
 > rustup toolchain install nightly
 > rustup default nightly
 > ```
 >
+> or only for this project
+>
+> > ```bash
+> rustup toolchain install nightly
+> cd <into your project>
+> rustup override set nightly
+> ```
+>
+> [See here for more details.](https://doc.rust-lang.org/book/appendix-07-nightly-rust.html)
+> 
 > If you’d rather use stable Rust with Leptos, you can do that too. In the guide and examples, you’ll just use the [`ReadSignal::get()`](https://docs.rs/leptos/latest/leptos/struct.ReadSignal.html#impl-SignalGet%3CT%3E-for-ReadSignal%3CT%3E) and [`WriteSignal::set()`](https://docs.rs/leptos/latest/leptos/struct.WriteSignal.html#impl-SignalGet%3CT%3E-for-ReadSignal%3CT%3E) methods instead of calling signal getters and setters as functions.
 
 Make sure you've added the `wasm32-unknown-unknown` target so that Rust can compile your code to WebAssembly to run in the browser.

docs/book/src/view/04_iteration.md

@@ -51,7 +51,8 @@ The fact that the _list_ is static doesn’t mean the interface needs to be stat
 You can render dynamic items as part of a static list.
 
 ```rust
-// create a list of N signals
+// create a list of 5 signals
+let length = 5;
 let counters = (1..=length).map(|idx| create_signal(idx));
 
 // each item manages a reactive view