Added Process exercise's chapter

ex13.c

@@ -0,0 +1,23 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+int main(void)
+{
+  pid_t pid;
+  pid = fork();
+
+  if (pid < 0) {
+    fprintf(stderr, "Fork failed\n");
+    return 1;
+  } else if (pid == 0) {
+    execlp("/bin/ls", "ls", NULL);
+    printf("LINEA J\n");
+  } else {
+    wait(NULL);
+    printf("Child complete\n");
+  }
+
+  return 0;
+}