[Docs] Add Skills extension entry to CHANGELOG

Author: wachterjohannes

CHANGELOG.md

@@ -8,6 +8,7 @@ All notable changes to `mcp/sdk` will be documented in this file.
 * [BC Break] Remove the `providerClass` argument of `#[CompletionProvider]`. Use `provider:`, which takes the same class-string and is now the first positional argument.
 * Add `HttpTransport::getSessionId()` to read the server-minted `Mcp-Session-Id`: a request-scoped caller can persist it and pass it back through the constructor's `$headers` on a later transport. Always `null` on `2026-07-28`, which removed protocol-level sessions.
 * Fix OIDC discovery rejecting issuers with a trailing slash (e.g. Authentik, Auth0).
+* Add the Skills extension (`io.modelcontextprotocol/skills`, SEP-2640). `Builder::addSkillsFromDirectory()` serves a directory of `SKILL.md` skills as `skill://` resources, and `skills/list`/`skills/get` answer with a complete, digest-and-size manifest per skill.
 
 0.8.0
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