Add documentation for how to run the language server

[milesziemer]

Should have docs saying how to run the language server in a few different ways:

• Manually, directly from the jar (download from https://github.com/smithy-lang/smithy-language-server/releases, JDK 21 requirement, passing port argument)
• Using Neovim (can point to https://github.com/neovim/nvim-lspconfig/blob/master/doc/configs.md#smithy_ls, also note JDK 21 requirement)
• Using VSCode (just point to the vscode extension)