Micro: added initial documentation

docs/micro.md

@@ -0,0 +1,28 @@
+You must add the following code to your `init.lua`:
+
+```lua
+local buffer = import("micro/buffer")
+local shell = import("micro/shell")
+
+function vivifyOpen(buf)
+    local cursor = buf:GetActiveCursor()
+    local line = cursor.Loc.Y + 1
+
+    shell.ExecCommand("viv", string.format("%s:%d", buf.AbsPath, line))
+end
+
+function onBufferOpen(buf)
+    if os.getenv("MICRO_VIVIFY") ~= "1" then
+        return
+    end
+
+    if buf.Type.Kind == buffer.BTDefault then
+        vivifyOpen(buf)
+    end
+end
+```
+
+This enables Vivify to run automatically when a file is opened, effectively simulating “startup” behavior (since Micro does not provide a true startup command hook for this use case).
+
+Big thanks to @Andriamanitra for answering [my questions](https://github.com/micro-editor/micro/discussions/4078).
+