docs: add parallel rail section and split config page (#1295)

Author: miyoungc

docs/index.md

@@ -26,7 +26,7 @@ release-notes.md
 :name: Common Tasks
 :hidden:
 
-user-guides/configuration-guide
+user-guides/configuration-guide/index
 user-guides/guardrails-library
 user-guides/guardrails-process
 user-guides/colang-language-syntax-guide

docs/release-notes.md

@@ -12,6 +12,16 @@ The following sections summarize and highlight the changes for each release.
 For a complete record of changes in a release, refer to the
 [CHANGELOG.md](https://github.com/NVIDIA/NeMo-Guardrails/blob/develop/CHANGELOG.md) in the GitHub repository.
 
+(v0-15-0)=
+
+## 0.15.0
+
+(v0-15-0-features)=
+
+### Features
+
+- Added parallel execution for input and output rails. To learn more, refer to [](parallel-rails).
+
 (v0-14-1)=
 
 ## 0.14.1