NETSCRIPT: Add the 'cat' method to 'ns.singularity' (#1999)

src/ScriptEditor/NetscriptDefinitions.d.ts

@@ -2656,6 +2656,15 @@ export interface Singularity {
    */
   getCurrentServer(): string;
 
+  /**
+   * Displays the content of a file on the currently connected server.
+   * @remarks
+   * RAM cost: 0.5 * 16/4/1
+   *
+   * @param filename - Name of the file to display, including its extension.
+   */
+  cat(filename: string): void;
+
   /**
    * Connect to a server.
    * @remarks