Replace README.txt with README.md

Patch is working and marking it to RTBC.

Chesterr → made their first commit to this issue’s fork.

Thanks all for your contribution

Since in MR too many commits for so minor change I've decided to override all commits. Did rebase with development branch and committed all changes from @manoj-rajr and @Cheasterr in a single commit.

Automatically closed - issue fixed for 2 weeks with no activity.