如何提示用户下载进程？

#### Before Issue

1. Please search on the [Issues](https://github.com/lingochamp/FileDownloader/issues)
2. Please search on the [wiki](https://github.com/lingochamp/FileDownloader/wiki)
3. Please set `FileDownloadLog.NEED_LOG=true` and review the Logcat output from main process and `:filedownloader` process ( pay attention to Warn and Error level logcat)

#### Issue

1. What problem do you get?
2. Which version of FileDownloader are you using when you produce such problem?
3. How to reproduce such problem?
4. Do you set `FileDownloadLog.NEED_LOG=true`?
5. Could you please reproduce this problem and provide all main process and `:filedownloader` process logcat
6. Can you fix it by yourself and request PR, if not, what's problem do you get when you try to fix it

>P.S. If you don't know how to get `:filedownloader` process, it's recommended to using `pidcat` to just filter all your application logcat, or define `process.non-separate=true` on [filedownloader.properties](https://github.com/lingochamp/FileDownloader/wiki/filedownloader.properties)

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请在Issue前认真的跟进上面提到的建议，这样将可以极大的加快你遇到问题的处理。

The body contains only the issue template and no concrete reproduction, version, logs, files, or tests. Start by clarifying what user download progress should be shown and how to reproduce the current behavior; completion would require an agreed expected result and implementation scope.

Written by the indexing model from the issue text.