cmd/shfmt: move --filename out of parser options

The man page says:

    If any parser or printer flags are given to the tool,
    no EditorConfig formatting options will be used.

This clearly does not apply to --filename, which primarily exists
so that stdin inputs can still use EditorConfig filename matching.

While here, add a note about EditorConfig support to the help text,
which wasn't obvious unless the user went to read `man shfmt`.

Fixes #1079.

cmd/shfmt/main.go

@@ -136,12 +136,12 @@ directory, all shell scripts found under that directory will be used.
   -s,  --simplify  simplify the code
   -mn, --minify    minify the code to reduce its size (implies -s)
   --apply-ignore   always apply EditorConfig ignore rules
+  --filename str   provide a name for the standard input file
 
 Parser options:
 
   -ln, --language-dialect str  bash/posix/mksh/bats, default "auto"
   -p,  --posix                 shorthand for -ln=posix
-  --filename str               provide a name for the standard input file
 
 Printer options:
 
@@ -158,7 +158,9 @@ Utilities:
   --to-json    print syntax tree to stdout as a typed JSON
   --from-json  read syntax tree from stdin as a typed JSON
 
-For more information, see 'man shfmt' and https://github.com/mvdan/sh.
+Formatting options can also be read from EditorConfig files; see 'man shfmt'
+for a detailed description of the tool's behavior.
+For more information and to report bugs, see https://github.com/mvdan/sh.
 `)
 	}
 	flag.Parse()

cmd/shfmt/shfmt.1.scd

@@ -54,6 +54,12 @@ predictable. Some aspects of the format can be configured via printer flags.
 	Should be useful to any tools or editors which format stdin or a single file.
 	When printing results to stdout, an ignored file results in no output at all.
 
+*--filename* str
+	Provide a name for the standard input file.
+
+	Use of this flag is necessary for EditorConfig support to work with stdin,
+	since EditorConfig files are found relative to the location of a script.
+
 ## Parser flags
 
 *-ln*, *--language-dialect* <str>
@@ -70,12 +76,6 @@ predictable. Some aspects of the format can be configured via printer flags.
 *-p*, *--posix*
 	Shorthand for *-ln=posix*.
 
-*--filename* str
-	Provide a name for the standard input file.
-
-	Use of this flag is necessary for EditorConfig support to work with stdin,
-	since EditorConfig files are found relative to the location of a script.
-
 ## Printer flags
 
 *-i*, *--indent* <uint>