copyurl: add troubleshooting section to the docs

See: https://forum.rclone.org/t/copyurl-fails-with-stream-error-wget-and-curl-works/44382/2

cmd/copyurl/copyurl.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"strings"
 
 	"github.com/rclone/rclone/cmd"
 	"github.com/rclone/rclone/fs"
@@ -34,23 +35,37 @@ func init() {
 
 var commandDefinition = &cobra.Command{
 	Use:   "copyurl https://example.com dest:path",
-	Short: `Copy url content to dest.`,
+	Short: `Copy the contents of the URL supplied content to dest:path.`,
-	Long: `
+	Long: strings.ReplaceAll(`
 Download a URL's content and copy it to the destination without saving
 it in temporary storage.
 
-Setting ` + "`--auto-filename`" + ` will attempt to automatically determine the filename from the URL
+Setting |--auto-filename| will attempt to automatically determine the
-(after any redirections) and used in the destination path. 
+filename from the URL (after any redirections) and used in the
-With ` + "`--auto-filename-header`" + ` in 
+destination path.
-addition, if a specific filename is set in HTTP headers, it will be used instead of the name from the URL.
-With ` + "`--print-filename`" + ` in addition, the resulting file name will be printed.
 
-Setting ` + "`--no-clobber`" + ` will prevent overwriting file on the 
+With |--auto-filename-header| in addition, if a specific filename is
+set in HTTP headers, it will be used instead of the name from the URL.
+With |--print-filename| in addition, the resulting file name will be
+printed.
+
+Setting |--no-clobber| will prevent overwriting file on the 
 destination if there is one with the same name.
 
-Setting ` + "`--stdout`" + ` or making the output file name ` + "`-`" + `
+Setting |--stdout| or making the output file name |-|
 will cause the output to be written to standard output.
-`,
+
+### Troublshooting
+
+If you can't get |rclone copyurl| to work then here are some things you can try:
+
+- |--disable-http2| rclone will use HTTP2 if available - try disabling it
+- |--bind 0.0.0.0| rclone will use IPv6 if available - try disabling it
+- |--bind ::0| to disable IPv4
+- |--user agent curl| - some sites have whitelists for curl's user-agent - try that
+- Make sure the site works with |curl| directly
+
+`, "|", "`"),
 	Annotations: map[string]string{
 		"versionIntroduced": "v1.43",
 		"groups":            "Important",