README.md: add Alternatives section

[vitaly-zdanevich]

I love to add cross-references. But I think KeePass will not accept my PR to mention this repo :(

[yitsushi]

If we add alternatives, the list would be a loooooot longer and I don't even think keepassxc is an alternative to this project. That's a password manager that has totp capabilities, but most if not all password managers has totp capabilities. I don't think adding that to the readme has any value. Adding tools like oathtool, WhyNotHugo/totp-cli, Google Authenticator, Authy, or even aram-hamo/totp-cli (which is a wrapper around oathtool) would have some value, but adding a password manager is like saying Chrome and Firefox are alternatives to wget and curl, indeed they both can download a webpage, but I wouldn't say they are alternatives to each other.

This project is not and will not be a password manager, only totp tokens following the gnu principal of "doing one thing that can be combined with other tools and do not try to do more things".

In my opinion if you say something is an alternative solution to something, you can create a table with various features to list which one is implemented in each of them, and show how good or bad the implementation is. For totp you can list only one thing that you can split up if you try very hard like "store totp secret token", "generate totp token from secret", "delete stored totp secret token". But that's it. For keepassxc that list is a lot longer and 90% of it is totally irrelevant to totp-cli.

From the front page:

• KeePassXC: Cross-platform Password Manager
• totp-cli: Authy/Google Authenticator like TOTP CLI tool written in Go.

[yitsushi]

We can add an Alternatives section, I'm happy to include them, but only with alternative tools, tools living in the same space, and not tools/programs that has similar functionality as a tiny fraction of their full set of features. For example lists see previous comment.

What is not an alternative software: LastPass, Bitwarden, KeePass, etc.