[Loading] Link tech talk slides from README.md

Put a link for slides describing the relationship between the fetch spec
and Chromium loading implementation from some README.md files.

Bug: None
Change-Id: I21cdc8cd005f74152e7908dfb58a1b34b7041d32
No-Try: True
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2298886
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#788533}

services/network/README.md

@@ -27,6 +27,7 @@ https://docs.google.com/document/d/1wAHLw9h7gGuqJNCgG1mP1BmLtCGfZ2pys-PdZQ1vg7M/
 # Related docs
 
 * [URLLoader](url_loader.md)
+* [Slides describing the relationship with the fetch spec](https://docs.google.com/presentation/d/1r9KHuYbNlgqQ6UABAMiWz0ONTpSTnMaDJ8UeYZGWjls/)
 
 # Where does the network service run?
 

third_party/blink/renderer/platform/loader/README.md

@@ -15,6 +15,10 @@ Contains files for low-level loading APIs.  The `PLATFORM_EXPORT` macro is
 needed to use them from `core/`.  Otherwise they can be used only in
 `platform/`.
 
+The directory conceptually implements https://fetch.spec.whatwg.org/#fetching
+(with lower-level components such as the network service). See also: [slides
+describing the relationship with the fetch spec](https://docs.google.com/presentation/d/1r9KHuYbNlgqQ6UABAMiWz0ONTpSTnMaDJ8UeYZGWjls/)
+
 ## testing
 
 Contains helper files for testing that are available in both