AW docs: document secure folder caveat

This adds info about work profile and Samsung Secure Folder and how to
work around these when switching WebView provider.

Fixed: 1092497
Test: Upload to gerrit > open file > click "gitiles"
Change-Id: Iac02758b9772962b7949c267c52919e43f415204
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2237048
Commit-Queue: Richard Coles <torne@chromium.org>
Reviewed-by: Richard Coles <torne@chromium.org>
Auto-Submit: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#777350}

android_webview/docs/prerelease.md

@@ -131,6 +131,31 @@ Any WebView-related bugs can be filed
 To best enable us to resolve the issue, please ensure you provide all of the
 information requested in the bug report template.
 
+## Work profile, multiple users, or Samsung Secure Folder
+
+*** aside
+This only applies to Android 8 (Oreo) and above.
+***
+
+If your Android device has been configured with a work profile, you'll need to
+install pre-release WebView for both your work profile and regular profile. You
+can only change WebView channel if you've enabled this for all profiles on the
+device. Then you should be able to successfully switch WebView channels
+following the steps above.
+
+Some devices [may support multiple user
+accounts](https://support.google.com/nexus/answer/2865483?hl=en). Similar to
+work profile, your pre-release WebView channel must be installed and enabled for
+each user account on the device.
+
+Some Samsung phones support a feature called [Secure
+Folder](https://www.samsung.com/global/galaxy/what-is/secure-folder/). Under the
+hood, this is implemented by creating a new user profile, similar to work
+profile or multiple users. If you've previously enabled the Secure Folder
+feature, you'll need to add your WebView channel to the folder. Open the folder,
+click "add apps," and select the desired WebView channel. Then you should be
+able to select WebView from the menu above.
+
 ## Command line tools
 
 Choosing your WebView implementation on Android 7 (Nougat) or later can also