Add explainer document for technologies used

[victorhuangwq]

Add an explainer document on the following:

WebView2Utilities uses documented regkeys, env vars (loader override regkeys and env vars), and paths (Edge install paths). It also uses some things not explicitly in our documentation but perhaps implied like knowing that WebView2 (based on Edge which is based on chromium) uses chromium IPC which uses Windows named pipes to communicate between processes (wv2util will use that to figure out how processes are connected), or the chromium Window style name, or the chromium-style browser command line arguments (eg --type=renderer, --user-data-dir=C:..., and so on - documented by chromium).