docs: add release-notes LND 0.21.0

Author: ziggie1984

docs/release-notes/release-notes-0.21.0.md

@@ -0,0 +1,55 @@
+# Release Notes
+- [Bug Fixes](#bug-fixes)
+- [New Features](#new-features)
+    - [Functional Enhancements](#functional-enhancements)
+    - [RPC Additions](#rpc-additions)
+    - [lncli Additions](#lncli-additions)
+- [Improvements](#improvements)
+    - [Functional Updates](#functional-updates)
+    - [RPC Updates](#rpc-updates)
+    - [lncli Updates](#lncli-updates)
+    - [Breaking Changes](#breaking-changes)
+    - [Performance Improvements](#performance-improvements)
+    - [Deprecations](#deprecations)
+- [Technical and Architectural Updates](#technical-and-architectural-updates)
+    - [BOLT Spec Updates](#bolt-spec-updates)
+    - [Testing](#testing)
+    - [Database](#database)
+    - [Code Health](#code-health)
+    - [Tooling and Documentation](#tooling-and-documentation)
+- [Contributors (Alphabetical Order)](#Contributors)
+
+# Bug Fixes
+
+# New Features
+## Functional Enhancements
+
+## RPC Additions
+
+## lncli Additions
+
+# Improvements
+## Functional Updates
+
+## RPC Updates
+
+## lncli Updates
+
+## Code Health
+
+## Breaking Changes
+
+## Performance Improvements
+
+## Deprecations
+
+# Technical and Architectural Updates
+## BOLT Spec Updates
+
+## Testing
+
+## Code Health
+
+## Tooling and Documentation
+
+# Contributors (Alphabetical Order)