Add Web UI main screenshot to English and Russian doc landing pages.

Show the console on the root READMEs and docs indexes, with a link to the
full Web UI guide at the bottom.

docs/README.md

@@ -5,6 +5,8 @@
 Guides for the oVirt / RHV Engine API simulator. Switch language with the header
 on each page. Russian mirrors live under [`ru/`](ru/README.md).
 
+![Web UI main](images/web-ui/console.png)
+
 | Guide | Description |
 |---|---|
 | [Getting started](getting-started.md) | First successful lab session |
@@ -29,3 +31,5 @@ on each page. Russian mirrors live under [`ru/`](ru/README.md).
 Runnable cookbooks: [`examples/`](../examples/README.md).  
 Integration suites: [`pulumi-tests/`](../pulumi-tests/README.md).  
 Contract packs: [`contracts/`](../contracts/README.md).
+
+More screens and details: [Web UI](web-ui.md).