WG Charter: expand WebAppSec citation

[xfq]

Fix #77.

[samuelweiler]

Sorry; this still is not clear to me.

Try with some different words? Feel free to try to explain here or in #77

[xfq]

The following work might need technical coordination between the MiniApps WG and the WebAppSec WG:

1. There is a reqPermissions array in the manifest spec used for declaring permissions, so it might be related to the work in the Permissions API.

2. Some sensitive APIs the group might develop in the future (see also Elements and APIs in the charter scope #79) should be gated by a request for user consent and be delivered only in secure contexts, so they might be related to the work in the Permissions API and Secure Contexts specs.

3. There might be need for fine-grained control over features (there's no plan now, so I'm just guessing), so Feature Policy might be related too.

Is it clear now?

[xfq]

I just modified the text since we do not plan to standardize device APIs for now per https://www.w3.org/2020/07/09-miniapp-minutes.html#t03

Merging this PR. Feel free to reopen #77 (or create a new issue) if you are not content with the text. @samuelweiler

FYI - I also opened an issue about the permission model of MiniApps. See #117.