Fix logo link in README

Author: lifei07

README.md

@@ -1,4 +1,4 @@
-# ![QUICKPIC](http://exodus.physics.ucla.edu/~uclapic/repo_images/quickpic.png)
+# ![QUICKPIC](https://ucla-plasma-simulation-group.github.io/QuickPIC-OpenSource/media/quickpic_logo.png)
 QuickPIC is a 3D parallel (MPI & OpenMP Hybrid) Quasi-Static PIC code, which is developed based on the framework UPIC. QuickPIC can efficiently simulate plasma based accelerator problems. This is the UCLA Plasma Simulation Group's official open-source repository for QuickPIC.
 
 # Upon cloning the repository
@@ -11,4 +11,4 @@ Please feel free to join in our email list [quickpic-users-developers](https://g
 
 * [Installation](https://github.com/UCLA-Plasma-Simulation-Group/QuickPIC-OpenSource/wiki/Install-QuickPIC)
 * [Input file](https://github.com/UCLA-Plasma-Simulation-Group/QuickPIC-OpenSource/wiki/Input-File-for-QuickPIC)
-* [Developer Guide](https://ucla-plasma-simulation-group.github.io/QuickPIC-OpenSource/) 
+* [Developer Guide](https://ucla-plasma-simulation-group.github.io/QuickPIC-OpenSource/)