docs: Clarify Skills feature vs slash commands in changelog

Update the 2.0.20 changelog entry to explain that:
- Skills is a new feature for specialized capabilities
- The Skill tool also handles slash command invocation
- This is an internal change, not a replacement of slash commands
- Slash commands continue to work the same way for users

This addresses confusion where people thought slash commands were
being replaced with skills.

CHANGELOG.md

@@ -370,7 +370,7 @@
 
 ## 2.0.20
 
-- Added support for Claude Skills
+- Added support for Claude Skills. Skills are a new feature that provide specialized capabilities and domain knowledge to Claude. The internal "Skill" tool also handles slash command invocation (previously done by the "SlashCommand" tool) - this is an internal change to how Claude invokes your slash commands, not a replacement of slash commands. Slash commands continue to work exactly the same way for users.
 
 ## 2.0.19