updating DIRECTORY.md

Author: cclauss

DIRECTORY.md

@@ -479,6 +479,7 @@
   * [Ic 555 Timer](electronics/ic_555_timer.py)
   * [Ind Reactance](electronics/ind_reactance.py)
   * [Ohms Law](electronics/ohms_law.py)
+  * [Power Factor Correction](electronics/power_factor_correction.py)
   * [Real And Reactive Power](electronics/real_and_reactive_power.py)
   * [Resistor Color Code](electronics/resistor_color_code.py)
   * [Resistor Equivalence](electronics/resistor_equivalence.py)
@@ -876,6 +877,7 @@
   * [Test Factorial](maths/test_factorial.py)
   * [Test Prime Check](maths/test_prime_check.py)
   * [Three Sum](maths/three_sum.py)
+  * [Tonelli Shanks](maths/tonelli_shanks.py)
   * [Trailing Zeroes](maths/trailing_zeroes.py)
   * [Trapezoidal Rule](maths/trapezoidal_rule.py)
   * [Triplet Sum](maths/triplet_sum.py)