chore(docs): Update README.md (nvim-lua#1344)

Neovim has renamed the "linux64" binary to "linux-x86_64".

Author: rnevius

README.md

@@ -219,7 +219,7 @@ sudo chmod a+rX /opt/nvim-linux64
 sudo tar -C /opt -xzf nvim-linux64.tar.gz
 
 # make it available in /usr/local/bin, distro installs to /usr/bin
-sudo ln -sf /opt/nvim-linux64/bin/nvim /usr/local/bin/
+sudo ln -sf /opt/nvim-linux-x86_64/bin/nvim /usr/local/bin/
 ```
 </details>
 <details><summary>Fedora Install Steps</summary>