Improve Instructions in Languages.md for adding new Languages

[Prakhar-Agarwal-byte]

Describe the issue In the Languages.md file 2 points can be improved:

1. In point 1 the value of string should not be "hi-rIN",

   <string name="language_hi_key" translatable="false">hi-rIN</string>

   but it should be "hi", only then it would work.

   <string name="language_hi_key" translatable="false">hi</string>

2. In point 2 we can be more specific, to avoid any confusion, and change the point from

   Add `language_hi` key in every strings file.

   to

   Add `language_hi` key in every strings file, translated into their respective language. For Example, in `strings.xml (hi)` add ```<string name="language_hi">हिंदी </string```

Additional context Many people were commiting the same mistake so I thought we can change the instructions a bit to reduce confusion.