Update architecture documentation to include NoHitLRU scoring.

Signed-off-by: usize <mofoster@redhat.com>

Author: usize

docs/architecture.md

@@ -364,6 +364,57 @@ used for the same session.
 
 ---
 
+#### NoHitLRUScorer
+
+Scores pods based on least recently used (LRU) ordering for cold requests (requests with no KV cache hits).
+This helps evenly distribute cache growth across pods, since cold requests result in new KV blocks being created.
+
+The scorer integrates with a prefix cache plugin to determine if a request has cache hits:
+- For cold requests (no cache hits): Ranks pods by LRU order, with never-used or least recently used pods
+  receiving higher scores (up to 1.0) and most recently used pods receiving lower scores (approaching 0.0)
+- For warm requests (cache hits): Returns neutral scores (0.5) for all pods to avoid interfering with
+  cache locality optimization
+
+The LRU tracking is specific to cold requests only - pods are added to the LRU cache when they serve
+a cold request, not when they serve requests with cache hits.
+
+- **Type**: `no-hit-lru-scorer`
+- **Parameters**:
+  - `prefixPluginName` (optional): The name of the prefix cache plugin to read state from. Defaults to `prefix-cache-scorer`.
+  - `lruSize` (optional): The maximum number of pods to track in the LRU cache. Defaults to 1024.
+
+Example configuration:
+
+```yaml
+plugins:
+  - type: prefix-cache-scorer
+    parameters:
+      hashBlockSize: 5
+      maxPrefixBlocksToMatch: 256
+      lruCapacityPerServer: 31250
+  - type: no-hit-lru-scorer
+    parameters:
+      lruSize: 2048
+  - type: decode-filter
+  - type: max-score-picker
+  - type: single-profile-handler
+schedulingProfiles:
+  - name: default
+    plugins:
+      - pluginRef: decode-filter
+      - pluginRef: max-score-picker
+      - pluginRef: prefix-cache-scorer
+        weight: 2
+      - pluginRef: no-hit-lru-scorer
+        weight: 1
+```
+
+**Note:** This scorer is designed to work alongside a prefix cache scorer (such as `prefix-cache-scorer` or
+`precise-prefix-cache-scorer`). If no prefix cache state is available, all requests are treated as cold.
+When integrating with a prefix-cache scorer, the prefix-cache scorer should be defined first in the scheduling profile.
+
+---
+
 ### Sample Disaggregated Prefill/Decode Configuration
 
 The following is an example of what a configuration for disaggregated Prefill/Decode might look like: