[Documentation] README: Activate Badges and Fix Two Obvious Bugs

[kevinmatthes]

This PR fixes the following documentation bugs:

• the license badge was configured but not activated
• a description in the README missed a trailing full stop
• the download instruction was taken from another project but not adjusted

The commit description uses the CHANGELOG artifact format Aeruginous v1.1.0+ supports; Aeruginous can create you a CHANGELOG from your commit messages. Shall I configure this for your project?

This is a very interesting project in the spirit of early Excel versions. I hope there will be a release to crates.io in the future.

[wert007]

The commit description uses the CHANGELOG artifact format Aeruginous v1.1.0+ supports; Aeruginous can create you a CHANGELOG from your commit messages. Shall I configure this for your project?

Hmm, no, I think it is way too early for that. The project needs to mature more for that in my opinion.

And yes you caught me, I copied a lot from another repository, thanks for catching my mistakes!