jailer: document FD inheritance changes
update CHANGELOG.md and docs/jailer.md with jailer changes
# Changelog
+## [Unreleased]
+
+### Changed
+
+- Dropped the JSON-formatted `context` command-line parameter from Firecracker
+ in favor of individual classic command-line parameters.
+- When running with `jailer` the location of the API socket has changed to
+ `<jail-root-path>/api.socket` (API socket was moved _inside_ the jail).
+
## [0.15.0]
### Added
