feat(search): Add sad.nvim (#427)

lua/astrocommunity/search/sad-nvim/README.md

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+# sad.nvim
+
+Space Age seD in Neovim. A project-wide find and replace plugin for Neovim.
+
+Requires:
+- [sad](https://github.com/ms-jpq/sad#get-sad-now)
+- [fzf](https://github.com/junegunn/fzf) so you can confirm/select the matches to apply your changes
+- by default the plugin using [fd](https://github.com/sharkdp/fd) to list all files in the current folder, you can use
+  `git ls_file`
+- a pager tool, e.g. `delta`
+
+**Repository:** <https://github.com/ray-x/sad.nvim>

lua/astrocommunity/search/sad-nvim/init.lua

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+return {
+  "ray-x/sad.nvim",
+  dependencies = { "ray-x/guihua.lua", build = "cd lua/fzy && make" },
+  opts = {},
+  event = "User AstroFile",
+  cmd = { "Sad" },
+}