Added Explanation for Array Push (#1328)

Basic information on the push method with example. How to use it and when to use it.

src/pages/javascript/standard-objects/array/array-prototype-push/index.md

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 #### More Information:
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+### Basic Information:
+This is a method on Array's to add elements on the end of the an array.
 
+`var myStarkFamily = ['John', 'Sansa', 'Brian'];`
+
+### Explanation:
+Now I have an array which contains members of Stark family from Game of thrones. But you can see that one of the member is missing.
+That is **Arya** and I want to add it.
+At this moment I know the length of an Array which is 3.
+So I can add it as follows:
+
+`myStarkFamily[3] = 'Arya';`
+
+Yes you can add it this way. But what if you donot know the length of and Array and want to add an element at the end.
+Then you do it as follows:
+
+`myStackFamily.push('Arya');`
+This returns you the new length of the array i.e. 4 and **Arya** is added to your Stark Family Array.
+Hence when you `console.log(myStarkFamily);` Your output is: `['John', 'Sansa', 'Brian', 'Arya'];`
+
+### In which case to use it:
+From above explanation it is clear that, you can use it in following case:
+1) When you want to add an element at the end of an Array.
+2) And you do not know how many elements are there in an array. So you can use push() on the array an pass the value you want to add.