feat(docs): add installation instructions for arch linux
feat(docs): add installation instructions for arch linux

closes #988

autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim