add gif in README.md

src/main.rs

@@ -2,8 +2,8 @@ use physarum::model;
 
 fn main() {
     // # of iterations to go through
-    // let n_iterations = 1024;
-    let n_iterations = 2048;
+    let n_iterations = 1024;
+    // let n_iterations = 2048;
 
     // Size of grid and pictures
     let (width, height) = (256, 256);