update README

README.md

@@ -12,7 +12,7 @@ Following is an example
 ## Requirements
 
 - [git](https://git-scm.com/book/en/v2/Getting-Started-Installing-Git) installed and is available in the PATH environment
-- privilege to the repository for uploading your images
+- privilege to the repository for uploading your images, and it should be public
 
 ## How to use
 
@@ -22,4 +22,6 @@ Make sure the requirements is satisfied, for the first time to use MarkdownImage
 
 Windows users can download MarkdownImageUploader_win_x64.exe from [here](https://github.com/WuLC/MarkdownImageUploader/releases/), it should be working on win7_x64 and win10_x64, which I have tested. 
 
-For Linux or Mac users, install [PySimpleGUI](https://github.com/PySimpleGUI/PySimpleGUI) with `pip install PySimpleGUI`, then run the script `python main.py` as a background program. But PySimpleGUI doesn't seem to work quite well with mac, and I'm not sure whether this work with mac.
+For Linux or Mac users, install [PySimpleGUI](https://github.com/PySimpleGUI/PySimpleGUI) with `pip install PySimpleGUI`, then run the script `python main.py` as a background program. But PySimpleGUI doesn't seem to work quite well with mac, and I'm not sure whether this work with mac.
+
+More details can be found in the [blog](http://wulc.me/2019/04/20/Markdown%20%E5%9B%BE%E7%89%87%E5%85%8D%E8%B4%B9%E4%B8%8A%E4%BC%A0%E5%B7%A5%E5%85%B7/)