readme: add newline after discord link
![Continuous Integration](https://github.com/managarm/mlibc/workflows/Continuous%20Integration/badge.svg)
**Official Discord server:** https://discord.gg/7WB6Ur3
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**AUR package** (provides `mlibc-gcc`): https://aur.archlinux.org/packages/mlibc
## Design of the library
