docs: readme, contributing guide

CONTRIBUTING.md

@@ -1 +1,70 @@
 # Contributing to tiny-debugger.nvim
+
+## Source Control
+
+We use **jj** (Jujutsu), not git. All commits should be made with `jj commit`.
+
+## Adding a New Adapter
+
+1. Create `lua/tiny-debugger/adapters/<language>.lua`
+2. Implement a `register(dap)` function that calls `loader.register()`
+3. Add the module name to the adapters list in `lua/tiny-debugger/adapters/init.lua`
+4. Add the language to the README and vimdoc tables
+
+Example adapter (minimal):
+
+```lua
+local loader = require("tiny-debugger.adapters.init")
+
+local M = {}
+
+function M.register(dap)
+  local binary = loader.find_executable({ "my-debug-adapter" })
+  if not binary then return end
+
+  loader.register(dap, "my-adapter", {
+    type = "executable",
+    command = binary,
+  }, {
+    {
+      type = "my-adapter",
+      request = "launch",
+      name = "Launch file",
+      program = "${file}",
+    },
+  }, { "mylang" })
+end
+
+return M
+```
+
+## Running Tests
+
+```sh
+nvim --headless -u tests/minimal_init.lua -c 'luafile tests/test_config.lua' -c 'qa!'
+nvim --headless -u tests/minimal_init.lua -c 'luafile tests/test_mode.lua' -c 'qa!'
+nvim --headless -u tests/minimal_init.lua -c 'luafile tests/test_keys.lua' -c 'qa!'
+nvim --headless -u tests/minimal_init.lua -c 'luafile tests/test_help.lua' -c 'qa!'
+nvim --headless -u tests/minimal_init.lua -c 'luafile tests/test_breakpoints.lua' -c 'qa!'
+nvim --headless -u tests/minimal_init.lua -c 'luafile tests/test_adapters.lua' -c 'qa!'
+```
+
+## Code Style
+
+- Clean, readable Lua. No metaprogramming tricks.
+- Every file should be short enough to read in one sitting.
+- No abstraction for abstraction's sake.
+- If a plugin does something we can do in <50 lines, we don't add the dependency.
+
+## Dependencies
+
+We depend on exactly five plugins (managed via `vim.pack.add`):
+
+- nvim-dap
+- nvim-dap-ui
+- nvim-nio
+- nvim-dap-virtual-text
+- persistent-breakpoints.nvim
+
+No language-specific plugin dependencies. Adapter configs are inlined as plain
+Lua tables.