readme: add --json

Author: sirupsen

README.md

@@ -183,6 +183,7 @@ Options:
   - `-d` or `--debug` - Print debug info
   - `-v` or `--verbose` - Print extra info
   - `-i` or `--interactive` - Confirm queries, implies `--debug`
+  - `---json` - Print JSONL output for machine readability
   - `--min-age` - Considers only rows older than specified.
                   Example: `--min-age=5min` ignores rows from the last 5 minutes.
                   Valid units: `d, days, h, hours, min, minutes, mon, months, s, seconds, w, weeks, y, years`