updated doc

Author: roulpriya

Documentation/SwiftlyDocs.docc/swiftly-cli-reference.md

@@ -23,7 +23,7 @@ swiftly [--version] [--help]
 Install a new toolchain.
 
 ```
-swiftly install [<version>] [--use] [--verify|no-verify] [--post-install-file=<post-install-file>] [--progress-file=<progress-file>] [--assume-yes] [--verbose] [--version] [--help]
+swiftly install [<version>] [--use] [--verify|no-verify] [--post-install-file=<post-install-file>] [--progress-file=<progress-file>] [--format=<format>] [--assume-yes] [--verbose] [--version] [--help]
 ```
 
 **version:**
@@ -89,6 +89,11 @@ Each progress entry contains timestamp, progress percentage, and a descriptive m
 The file must be writable, else an error will be thrown.
 
 
+**--format=\<format\>:**
+
+*Output format (text, json)*
+
+
 **--assume-yes:**
 
 *Disable confirmation prompts by assuming 'yes'*