Update documentation with reference link to Snell's Law

Added a reference link to Snell's Law in the documentation.

Author: Dsannue

src/main/java/com/thealgorithms/physics/SnellsLaw.java

@@ -3,6 +3,7 @@
 /**
  * Calculates refraction angle using Snell's Law:
  * n1 * sin(theta1) = n2 * sin(theta2)
+ * @see <a href="https://en.wikipedia.org/wiki/Snell%27s_law">Snell's Law</a>
  */
 public class SnellLaw {