docs: add `use_navigate` to router docs in guide

docs/book/src/router/19_a.md

@@ -18,6 +18,20 @@ The router also provides an [`<A>`](https://docs.rs/leptos_router/latest/leptos_
 1. Correctly resolves relative nested routes. Relative routing with ordinary `<a>` tags can be tricky. For example, if you have a route like `/post/:id`, `<A href="1">` will generate the correct relative route, but `<a href="1">` likely will not (depending on where it appears in your view.) `<A/>` resolves routes relative to the path of the nested route within which it appears.
 2. Sets the `aria-current` attribute to `page` if this link is the active link (i.e., it’s a link to the page you’re on). This is helpful for accessibility and for styling. For example, if you want to set the link a different color if it’s a link to the page you’re currently on, you can match this attribute with a CSS selector.
 
+## Navigating Programmatically
+
+Your most-used methods of navigating between pages should be with `<a>` and `<form>` elements or with the enhanced `<A/>` and `<Form/>` components. Using links and forms to navigate is the best solution for accessibility and graceful degradation.
+
+On occasion, though, you’ll want to navigate programmatically, i.e., call a function that can navigate to a new page. In that case, you should use the [`use_navigate`](https://docs.rs/leptos_router/latest/leptos_router/fn.use_navigate.html) function.
+```rust
+let navigate = leptos_router::use_navigate(cx);
+navigate("/somewhere", Default::default());
+```
+
+> You should almost never do something like `<button on:click=move |_| navigate(/* ... */)>`. Any `on:click` that navigates should be an `<a>`, for reasons of accessibility.
+
+The second argument here is a set of [`NavigateOptions`](https://docs.rs/leptos_router/latest/leptos_router/struct.NavigateOptions.html), which includes options to resolve the navigation relative to the current route as the `<A/>` component does, replace it in the navigation stack, include some navigation state, and maintain the current scroll state on navigation.
+
 > Once again, this is the same example. Check out the relative `<A/>` components, and take a look at the CSS in `index.html` to see the ARIA-based styling.
 
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