Missing documentation on dependencies, missing dependencies

I would like to test this game for https://github.com/luanti-org/luanti/issues/16986

**EDIT:** This is partially my fault. The game includes these mods, but does not state that the submodules need initializing. Please add that to the README.

However, I am greeted with this error:

```
ERROR[Main]: ServerError: Some mods have unsatisfied dependencies:
ERROR[Main]: - va_lobby is missing: bedrock2 barrier naturalslopeslib
ERROR[Main]: - va_terrain is missing: naturalslopeslib
ERROR[Main]: - va_weapons is missing: lightning
ERROR[Main]: Install and enable the required mods, or disable the mods causing errors.
```

Please document these in the README. After enabling these I get the following error:

```
ERROR[ServerStart]: Trying to register slopes for an unknown node saltd:burnt_branches
ERROR[Main]: ModError: Failed to load and run script from XXX/games/voxel_annihilation/mods/va_terrain/init.lua:
ERROR[Main]: ...XXX/mods/naturalslopeslib/init.lua:137: Attempt to override non-existent item saltd:burnt_trunk
ERROR[Main]: stack traceback:
ERROR[Main]: [C]: ?
ERROR[Main]: [C]: in function 'error'
ERROR[Main]: ...XXX/builtin/game/register.lua:465: in function 'old_override'
ERROR[Main]: ...XXX/mods/naturalslopeslib/init.lua:137: in function 'override_item'
ERROR[Main]: ...XXX/games/voxel_annihilation/mods/default/functions.lua:400: in function 'register_leafdecay'
ERROR[Main]: ...XXX/games/voxel_annihilation/mods/va_terrain/nodes.lua:355: in main chunk
```

Origin:
https://github.com/CryptechTest/voxel_annihilation/blob/46e397d5b30c13ef89dd7d602814b0b442cfd5c8/mods/va_terrain/nodes.lua#L354-L360

Needs a presence check whether the mod is present.