docs: document rich requires_env format and install-time prompting

Updates the plugin build guide and features page to reflect the
interactive env var prompting added in PR #5470. Documents the rich
manifest format (name/description/url/secret) alongside the simple
string format.

website/docs/guides/build-a-hermes-plugin.md

@@ -44,8 +44,12 @@ This tells Hermes: "I'm a plugin called calculator, I provide tools and hooks."
 Optional fields you could add:
 ```yaml
 author: Your Name
-requires_env:          # gate loading on env vars
+requires_env:          # gate loading on env vars; prompted during install
-  - SOME_API_KEY       # plugin disabled if missing
+  - SOME_API_KEY       # simple format — plugin disabled if missing
+  - name: OTHER_KEY    # rich format — shows description/url during install
+    description: "Key for the Other service"
+    url: "https://other.com/keys"
+    secret: true
 ```
 
 ## Step 3: Write the tool schemas
@@ -336,13 +340,35 @@ def register(ctx):
 If your plugin needs an API key:
 
 ```yaml
-# plugin.yaml
+# plugin.yaml — simple format (backwards-compatible)
 requires_env:
   - WEATHER_API_KEY
 ```
 
 If `WEATHER_API_KEY` isn't set, the plugin is disabled with a clear message. No crash, no error in the agent — just "Plugin weather disabled (missing: WEATHER_API_KEY)".
 
+When users run `hermes plugins install`, they're **prompted interactively** for any missing `requires_env` variables. Values are saved to `.env` automatically.
+
+For a better install experience, use the rich format with descriptions and signup URLs:
+
+```yaml
+# plugin.yaml — rich format
+requires_env:
+  - name: WEATHER_API_KEY
+    description: "API key for OpenWeather"
+    url: "https://openweathermap.org/api"
+    secret: true
+```
+
+| Field | Required | Description |
+|-------|----------|-------------|
+| `name` | Yes | Environment variable name |
+| `description` | No | Shown to user during install prompt |
+| `url` | No | Where to get the credential |
+| `secret` | No | If `true`, input is hidden (like a password field) |
+
+Both formats can be mixed in the same list. Already-set variables are skipped silently.
+
 ### Conditional tool availability
 
 For tools that depend on optional libraries:

website/docs/user-guide/features/plugins.md

@@ -87,7 +87,7 @@ Project-local plugins under `./.hermes/plugins/` are disabled by default. Enable
 | Inject messages | `ctx.inject_message(content, role="user")` — see [Injecting Messages](#injecting-messages) |
 | Ship data files | `Path(__file__).parent / "data" / "file.yaml"` |
 | Bundle skills | Copy `skill.md` to `~/.hermes/skills/` at load time |
-| Gate on env vars | `requires_env: [API_KEY]` in plugin.yaml |
+| Gate on env vars | `requires_env: [API_KEY]` in plugin.yaml — prompted during `hermes plugins install` |
 | Distribute via pip | `[project.entry-points."hermes_agent.plugins"]` |
 
 ## Plugin discovery