Update changelog for 0.6.1 (#249)

* Update changelog for 0.6.1

* Add JS mounting to description

* Update changelog

* Update changelog

* Fix API wording

* Fix unreleased

* Add note about contacting Modal

* Grammar

* Use past tense

Author: thomasjpfan

CHANGELOG.md

@@ -4,7 +4,7 @@ Both client libraries are pre-1.0, and they have separate versioning.
 
 ## Unreleased
 
-- Upgraded the internal handling of Sandbox exec to use the new command router interface, which brings greatly improved performance and reliability for exec operations.
+- Added custom domains to `Sandboxes.Create` in Go and `sandboxes.create` in JS. Note that Sandbox custom domains work differently from Function custom domains and must currently be set up manually by Modal; please get in touch if this feature interests you.
 
 ## modal-js/v0.6.0, modal-go/v0.6.0