Update README.md to include installation command for v4 (#66)

* Update README.md to include installation command for v4 

The README.md only had a single line for installation, but this line did not install the latest version of v4.1,0. I added this line to clarify to others how to get the latest version so there is no confusion.

* Stick to v4 installation instruction

Co-authored-by: Shivam Rathore <29069530+Shivam010@users.noreply.github.com>

Author: dc-dc-dc

README.md

@@ -32,7 +32,7 @@ clients is hearty welcome.
 
 ## Installation
 
-    go get github.com/nitishm/go-rejson
+    go get github.com/nitishm/go-rejson/v4
 
 ## Example usage