docs: better document the interaction of SsrModes with blocking resources (#1765)

Meant to address users making the same mistake as
https://github.com/leptos-rs/leptos/issues/1119

docs/book/src/ssr/23_ssr_modes.md

@@ -8,12 +8,12 @@ If you’ve ever listened to streaming music or watched a video online, I’m su
 
 Let me say a little more about what I mean.
 
-Leptos supports all four different modes of rendering HTML that includes asynchronous data:
+Leptos supports all the major ways of rendering HTML that includes asynchronous data:
 
 1. [Synchronous Rendering](#synchronous-rendering)
 1. [Async Rendering](#async-rendering)
 1. [In-Order streaming](#in-order-streaming)
-1. [Out-of-Order Streaming](#out-of-order-streaming)
+1. [Out-of-Order Streaming](#out-of-order-streaming) (and a partially-blocked variant)
 
 ## Synchronous Rendering
 
@@ -67,7 +67,7 @@ If you’re using server-side rendering, the synchronous mode is almost never wh
   - Able to show the fallback loading state and dynamically replace it, instead of showing blank sections for un-loaded data.
 - _Cons_: Requires JavaScript to be enabled for suspended fragments to appear in correct order. (This small chunk of JS streamed down in a `<script>` tag alongside the `<template>` tag that contains the rendered `<Suspense/>` fragment, so it does not need to load any additional JS files.)
 
-5. **Partially-blocked streaming**: “Partially-blocked” streaming is useful when you have multiple separate `<Suspense/>` components on the page. If one of them reads from one or more “blocking resources” (see below), the fallback will not be sent; rather, the server will wait until that `<Suspense/>` has resolved and then replace the fallback with the resolved fragment on the server, which means that it is included in the initial HTML response and appears even if JavaScript is disabled or not supported. Other `<Suspense/>` stream in out of order as usual.
+5. **Partially-blocked streaming**: “Partially-blocked” streaming is useful when you have multiple separate `<Suspense/>` components on the page.  It is triggered by setting `ssr=SsrMode::PartiallyBlocked` on a route, and depending on blocking resources within the view.   If one of the `<Suspense/>` components reads from one or more “blocking resources” (see below), the fallback will not be sent; rather, the server will wait until that `<Suspense/>` has resolved and then replace the fallback with the resolved fragment on the server, which means that it is included in the initial HTML response and appears even if JavaScript is disabled or not supported. Other `<Suspense/>` stream in out of order, similar to the `SsrMode::OutOfOrder` default.
 
 This is useful when you have multiple `<Suspense/>` on the page, and one is more important than the other: think of a blog post and comments, or product information and reviews. It is _not_ useful if there’s only one `<Suspense/>`, or if every `<Suspense/>` reads from blocking resources. In those cases it is a slower form of `async` rendering.
 
@@ -134,4 +134,23 @@ pub fn BlogPost() -> impl IntoView {
 }
 ```
 
-The first `<Suspense/>`, with the body of the blog post, will block my HTML stream, because it reads from a blocking resource. The second `<Suspense/>`, with the comments, will not block the stream. Blocking resources gave me exactly the power and granularity I needed to optimize my page for SEO and user experience.
+The first `<Suspense/>`, with the body of the blog post, will block my HTML stream, because it reads from a blocking resource.  Meta tags and other head elements awaiting the blocking resource will be rendered before the stream is sent.
+
+Combined with the following route definition, which uses `SsrMode::PartiallyBlocked`, the blocking resource will be fully rendered on the server side, making it accessible to users who disable WebAssembly or JavaScript.
+
+```rust
+<Routes>
+	// We’ll load the home page with out-of-order streaming and <Suspense/>
+	<Route path="" view=HomePage/>
+
+	// We'll load the posts with async rendering, so they can set
+	// the title and metadata *after* loading the data
+	<Route
+		path="/post/:id"
+		view=Post
+		ssr=SsrMode::PartiallyBlocked
+	/>
+</Routes>
+```
+
+The second `<Suspense/>`, with the comments, will not block the stream. Blocking resources gave me exactly the power and granularity I needed to optimize my page for SEO and user experience.