Update README.md with badges

[rakeshksr]

Following badges are added to README.md

• docs badge
• Tests badge
• codecov badge
• license badge
• Downloads badge

[codecov[bot]]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (4090805) 100.00% compared to head (5bd8192) 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #33 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 1 1 Lines 1 1 ========================================= Hits 1 1 ```

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[ashwani-rathee]

Looks good to me!