documentation: Add some basic readmes, clarify OWNERS.

Bug: 1099779
Change-Id: I877767ccc0fc7fad10cd2da9120413fd5db65a6a
Fixed: 1099779
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2323781
Auto-Submit: Joshua Pawlicki <waffles@chromium.org>
Reviewed-by: Sorin Jianu <sorin@chromium.org>
Commit-Queue: Sorin Jianu <sorin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792288}

components/client_update_protocol/README.md

+See [docs/updater/cup.md](../../docs/updater/cup.md).

components/component_updater/README.md

 # Component Updater
 
+[TOC]
+
 ## Overview
 The Component Updater is a piece of Chrome responsible for updating other pieces
 of Chrome. It runs in the browser process and communicates with a set of servers
@@ -24,7 +26,7 @@ For the purposes of this document:
    delivered by the component updater separately from the browser itself,
    usually as a dynamically-linked library or data file.
  * A `crx file` is any file in the
-   [CRX package format](https://developer.chrome.com/extensions/crx).
+   [CRX package format](../crx_file/README.md).
 
 ## Adding New Components
 This document covers the work that must be done on the client side. Additional

components/crx_file/OWNERS

-file://extensions/OWNERS
-
 waffles@chromium.org
 sorin@chromium.org
+
+# if the above are unavailable
+file://extensions/OWNERS
+
 # COMPONENT: Platform>Extensions

components/crx_file/README.md

+# CRX File
+
+The CRX File component is a collection of compilation units related to the
+creation or manipulation of CRX archive files.
+
+A CRX file is a ZIP archive with a prepended header section. The CRX file format
+is described in more detail in `crx3.proto`.
+
+`crx_creator.h` provides a means to create a CRX file.
+
+`crx_verifier.h` provides a means to verify the integrity of a CRX file.

components/update_client/README.md

+# Update Client
+
+Update Client is a reusable updater core that speaks the
+[Omaha 3.1 protocol](../../docs/updater/protocol_3_1.md). It powers the
+component and extension updaters, as well as the out-of-process updater in
+[chrome/updater](../../chrome/updater/README.md).
+
+The entry point to the library is `update_client.h`, and the comments in that
+file describe the library.