updated docs for at_contact library

[yahu1031]

- What I did

• Update the at_contact library documentation(README.md) W.R.T flutter

- How I did it

• Cloned, created branch, updated.

- How to verify it

• Head over to at_contact README.md

- Description for the changelog

Usage of the library update.

[yahu1031]

I need to get confirmation about the example app for this library.

[murali-shris]

keep the readme simple with only dart usage..flutter snippets can be part of at_contacts_flutter

[CynthiaPeter]

Can we change "Initially to get a basic overview of the @protocol packages, You must read the atsign docs." to

• To get a basic overview of the @protocol packages, Please visit the atsign developer docs to learn more. (Line 16)

• You need some basic setup to use this package. Follow our get started guide to set up. (Line 18)

Also, it is important we include tags and keywords.

[gkc]

@yahu1031 this was approved but not merged; shall you merge it to trunk?

[yahu1031]

@gkc Uh oh! Really sorry I thought it was merged. Lemme just go through the code again cause things have little changes from then to now.