Added readme.

README.md

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+# Lua Debugging TUI
+
+This is a text-based user interface command line debugging utility for Lua and Moonscript.
+It lets you browse the call stack, source code, and local variables right at the moment when
+your code crashes, or you call `ldt.breakpoint()`.
+
+## Requirements
+
+This library uses Curses via the [lcurses](https://github.com/rrthomas/lcurses) library
+and [LPeg](http://www.inf.puc-rio.br/~roberto/lpeg).
+
+## Usage
+
+To catch all errors inside a block of code, use:
+
+```Lua
+local ldt = require("ldt")
+ldt.guard(function()
+    -- Your crashing code here
+end)
+```
+
+To trigger a breakpoint, just add a call to `ldt.breakpoint()`. Also, you can use `ldt.hijack()`
+to replace `error()` and `assert()` with functions that will trigger the debugger. However,
+this is not recommended for general purpose debugging because Lua errors like trying to index
+a nil value do not call `error()`, so the debugger won't get triggered.
+
+## Navigation
+
+* Press 'q' to quit
+* Arrow keys or h/j/k/l for movement within the active pane (yellow border); scroll wheel also works, but only for vertical scrolling.
+* Press 'c' to select the call stack pane
+* Press 's' to select the source code pane (showing the source code for the file of the function selected in the callstack pane)
+* Press 'v' to select the variables pane (showing the variables at the selected level of the callstack)
+* Press 'd' to select the data pane (showing the value of the selected variable)