docs(is): correct grammar

subjects/is/README.md

@@ -2,30 +2,30 @@
 
 ### Instructions
 
-Add new function properties to the object `is` to check a value type
-
-- `is.num` value is a number
-- `is.nan` value is NaN
-- `is.str` value is a string
-- `is.bool` value is a boolean
-- `is.undef` value is undefined
-- `is.def` value is defined
-- `is.arr` value is an array
-- `is.obj` value is a simple object or null objects
-- `is.fun` value is a function
-- `is.truthy` value is truthy
-- `is.falsy` value is falsy
+Add new function properties to the `is` object to check value types. Each function should take one argument, and return a `boolean`.
+
+- `is.num`: value is a `number`.
+- `is.nan`: value is `NaN`.
+- `is.str`: value is a `string`.
+- `is.bool`: value is a `boolean`.
+- `is.undef`: value is `undefined`.
+- `is.def`: value is defined.
+- `is.arr`: value is an `array`.
+- `is.obj`: value is a simple object or `null` objects.
+- `is.fun`: value is a function.
+- `is.truthy`: value is truthy.
+- `is.falsy`: value is falsy.
 
 ### Notions
 
-- [nan-academy.github.io/js-training/examples/primitive-and-operators](https://nan-academy.github.io/js-training/examples/primitive-and-operators.js)
-- [devdocs.io/javascript/operators/typeof](https://devdocs.io/javascript/operators/typeof)
-- [developer.mozilla.org/en-US/docs/Glossary/Truthy](https://developer.mozilla.org/en-US/docs/Glossary/Truthy)
-- [developer.mozilla.org/en-US/docs/Glossary/Falsy](https://developer.mozilla.org/en-US/docs/Glossary/Falsy)
+- [Primitives and operators](https://nan-academy.github.io/js-training/examples/primitive-and-operators.js)
+- [typeof](https://devdocs.io/javascript/operators/typeof)
+- [Truthy](https://developer.mozilla.org/en-US/docs/Glossary/Truthy)
+- [Falsy](https://developer.mozilla.org/en-US/docs/Glossary/Falsy)
 
 ### Code provided
 
-> all code provided will be added to your solution and doesn't need to be submited.
+> The provided code will be added to your solution, and does not need to be submitted.
 
 ```js
 const is = {}