add readme

README.md

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+## Adds `/eval` command
+
+`/eval` takes lua code as argument and executes it. It will echo your command and show it's output and returned value.
+Each player gets their own "global" environment so they can't interfere with other user's envs by accident (exposed as `cmd_eval.e[player_name]`).
+
+## Some nice features:
+### Expression/statement agnostic
+This command:
+```
+/eval 1+2
+```
+Outputs this:
+```
+> 1+2
+| 3
+```
+
+This also just works:
+```
+> x = 2*2
+> x
+| 4
+```
+
+Multiple values also work:
+
+```
+> return 1,nil,3
+| 1,
+| nil,
+| 3
+```
+
+### Backtrace and error output
+Outputs both the error and clean backtrace (stack related only to provided code)
+
+### Print function
+No need to use `core.chat_send_player()`, just use `print()` - it will do the right thing.
+
+```
+> print(here)
+< (-98.0, 15.5, 33.4)
+```
+
+```
+> objs = core.get_objects_inside_radius(here, 10)
+> for i,o in ipairs(objs) do print(i, (o:get_luaentity() or {}).name, o:get_pos()) end
+< 1 nil (-98.0, 15.5, 33.4)
+< 2 mobs_animal:kitten (-101.0, 16.5, 30.0)
+< 3 mobs_animal:chicken (-92.0, 15.5, 34.2)
+```
+
+### "Magic" variables
+Some special variables are provided:
+- `here` - position where you executed the command
+- `me` - your player object
+- `point` - point in the world you're pointing at with your crosshair
+- `this_obj` - entity you're pointing at (can be `nil`)
+
+### Better output for arrays and some `userdata` objects
+```
+> me
+| #<player: "singleplayer">
+```
+
+Show indices for easier manual access:
+```
+> core.get_objects_inside_radius(here, 10)
+| {
+|  [1] = #<player: "singleplayer">,
+|  [2] = #<luaentity: "mobs_animal:kitten">,
+|  [3] = #<luaentity: "mobs_animal:chicken">,
+| }
+```
+
+### Keeping result of last /eval in `_` variable
+```
+> core.get_objects_inside_radius(here, 10)
+| {
+|  [1] = #<player: "singleplayer">,
+|  [2] = #<luaentity: "mobs_animal:kitten">,
+| }
+> _[2]
+| #<luaentity: "mobs_animal:kitten">
+> pos = _:get_pos()
+> pos
+| {
+|  x = 123.5,
+|  y = 15.0,
+|  z = 68.4
+| }
+```
+