[Condense] Add docs for intelligent condense experimental feature (#187)

Author: canrobins13

docs/features/experimental/experimental-features.md

@@ -18,6 +18,12 @@ To enable or disable experimental features:
 
 The following experimental features are currently available:
 
+### Intelligently condense the context window
+
+If enabled, Roo uses an LLM to summarize the past conversation when the context window is almost full. This summary attempts to dramatically shrink the number of tokens in the context while preserving useful information. If disabled, Roo drops past messages using a sliding window when the context window is full.
+
+**Disclaimer**: Currently the costs associated with summarizing the conversation are not included in the cost displayed in the UI.
+
 ### Power Steering
 
 When enabled, Roo will remind the model about the details of its current mode definition more frequently. This will lead to stronger adherence to role definitions and custom instructions, but will use more tokens per message.