Feat: Add zsh, fish and powershell completion support

See issue #4296

docs/content/en/commands/hugo_gen_autocomplete.md

@@ -1,5 +1,5 @@
 ---
-date: 2020-09-13
+date: 2021-01-06
 title: "hugo gen autocomplete"
 slug: hugo_gen_autocomplete
 url: /commands/hugo_gen_autocomplete/
@@ -12,9 +12,6 @@ Generate shell autocompletion script for Hugo
 
 Generates a shell autocompletion script for Hugo.
 
-NOTE: The current version supports Bash only.
-      This should work for *nix systems with Bash installed.
-
 By default, the file is written directly to /etc/bash_completion.d
 for convenience, and the command may need superuser rights, e.g.:
 
@@ -23,10 +20,13 @@ for convenience, and the command may need superuser rights, e.g.:
 Add `--completionfile=/path/to/file` flag to set alternative
 file-path and name.
 
+Add `--type={bash, zsh, fish or powershell}` flag to set alternative
+shell type.
+
 Logout and in again to reload the completion scripts,
 or just source them in directly:
 
-	$ . /etc/bash_completion
+	$ . /etc/bash_completion or /path/to/file
 
 ```
 hugo gen autocomplete [flags]
@@ -37,7 +37,7 @@ hugo gen autocomplete [flags]
 ```
       --completionfile string   autocompletion file (default "/etc/bash_completion.d/hugo.sh")
   -h, --help                    help for autocomplete
-      --type string             autocompletion type (currently only bash supported) (default "bash")
+      --type string             autocompletion type (zsh, bash, fish or powershell) (default "bash")
 ```
 
 ### Options inherited from parent commands
@@ -62,4 +62,4 @@ hugo gen autocomplete [flags]
 
 * [hugo gen](/commands/hugo_gen/)	 - A collection of several useful generators.
 
-###### Auto generated by spf13/cobra on 13-Sep-2020
+###### Auto generated by spf13/cobra on 6-Jan-2021