Added Parametric Equations and Polar Coordinates

This content isn't included in the Core Math Calculus Two course,
but it's necessary to learn it before moving on to Advanced Math
Multivariable Calculus. So the specific section is taken from
MIT's Single-variable Calculus is linked which saves us from needing
to change anything in Core CS.

Author: joshmhanson

README.md

@@ -311,6 +311,8 @@ Courses | Duration | Effort | Prerequisites
 
 **Topics covered**:
 `real analysis`
+`parametric equations`
+`polar coordinate systems`
 `multivariable integrals`
 `multivariable differentials`
 `probability theory`
@@ -319,8 +321,9 @@ Courses | Duration | Effort | Prerequisites
 Courses | Duration | Effort | Prerequisites
 :-- | :--: | :--: | :--:
 [Introduction to Mathematical Thinking](https://www.coursera.org/learn/mathematical-thinking) | 10 weeks | 10 hours/week | pre-calculus
-[Multivariable Calculus](https://ocw.mit.edu/courses/mathematics/18-02sc-multivariable-calculus-fall-2010/index.htm) | 13 weeks | 12 hours/week | single-variable calculus (Calculus Two)
-[Introduction to Probability - The Science of Uncertainty](https://www.edx.org/course/introduction-probability-science-mitx-6-041x-2) | 18 weeks | 12 hours/week | single- and multi-variable calculus
+[Calculus: Parametric Equations and Polar Coordinates](https://ocw.mit.edu/courses/mathematics/18-01sc-single-variable-calculus-fall-2010/unit-4-techniques-of-integration/part-c-parametric-equations-and-polar-coordinates/) | - | - | single-variable calculus (Calculus Two)
+[Multivariable Calculus](https://ocw.mit.edu/courses/mathematics/18-02sc-multivariable-calculus-fall-2010/index.htm) | 13 weeks | 12 hours/week | Parametric Equations and Polar Coordinates
+[Introduction to Probability - The Science of Uncertainty](https://www.edx.org/course/introduction-probability-science-mitx-6-041x-2) | 18 weeks | 12 hours/week | Multivariable Calculus
 
 ### Advanced systems