add celsiusToFahrenheit and fahrenheitToCelsius

snippets/celsiusToFahrenheit.md

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+### celsiusToFahrenheit
+
+Celsius to Fahrenheit temperature conversion.
+
+Follows the conversion formula `F =  1.8C + 32`
+```js
+const celsiusToFahrenheit = degrees => 1.8 * degrees + 32;
+```
+
+```js
+celsiusToFahrenheit(33) // '91.4'
+```

snippets/fahrenheitToCelsius.md

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+### fahrenheitToCelsius
+
+Fahrenheit to Celsius temperature conversion.
+
+Follows the conversion formula `C = (F - 32) * 5/9`
+```js
+const fahrenheitToCelsius = degrees => (degrees - 32) * 5/9;
+```
+
+```js
+fahrenheitToCelsius(32); // '0'
+```