doc: update installation guide to using new organization

haorenW1025 · haorenW1025 · commit 68ef6f0af0d4 · 2020-06-28T02:09:15.000+08:00
diff --git a/README.md b/README.md
@@ -28,7 +28,7 @@ make it a more user friendly without adding too much to it.
 - Install with any plugin manager by using the path on GitHub.
 
 ```vim
-Plug 'haorenW1025/diagnostic-nvim'
+Plug 'nvim-lua/diagnostic-nvim'
 ```
 
 ## Setup
