doc: make longer example collapsible (#857)

Author: nhat-vo

Diff for: README.md

@@ -95,6 +95,10 @@ Press `?` in the Neo-tree window to view the list of mappings.
 ## Quickstart
 
 #### Longer Example for Packer:
+<details>
+  <summary>
+    Click to view longer example for Packer.nvim
+  </summary>
 
 ```lua
 use {
@@ -440,7 +444,8 @@ use {
     end
 }
 ```
-
+</details>
+  
 _The above configuration is not everything that can be changed, it's just the
 parts you might want to change first._