add README

README.md

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+This library's purpose is to allow other mods to add growing things to the map in a straightforward, simple manner. It contains all the core functions needed by mods and modpacks such as More Trees, Tiny Trees, Plantlife, and others. 
+
+Spawning of plants is optionally sensitive to the amount of available light, elevation, nearness to other nodes, plant-to-plant density, water depth, and a whole host of controls. 
+
+All objects spawned or generated using this mod use Perlin noise to stay within simple biomes, rather than just letting everything just spread around the map randomly. 
+
+This library also features a basic temperature map, which should blend in nicely with SPlizard's Snow Biomes mod (the same Perlin settings are used, with the assumption that the edge of a snow biome is 0° Centigrade). 
+
+Both mapgen-based spawning and ABM-based spawning is supported. Growing code is strictly ABM-based. L-system trees can be spawned at mapgen time via the engine's spawn_tree() function and are quite fast.
+
+It is primarily intended for mapgen v6, but it should work fine when used with mapgen v7.
+
+**Dependencies**: default from minetest_game
+
+**Recommends**: [Plantlife Modpack](https://github.com/VanessaE/plantlife_modpack), 
+[More Trees](https://github.com/VanessaE/moretrees)
+
+**License**: WTFPL
+
+**API**: This mod supplies a small number of very powerful functions. They are, briefly:
+
+* biome_lib:register_generate_plant()
+* biome_lib:spawn_on_surfaces()
+* biome_lib:grow_plants()
+* biome_lib:find_valid_wall()
+* biome_lib:is_node_loaded()
+
+For a complete description of these functions as well as several of the internal variables within the mod, [read the API.txt document](https://raw.githubusercontent.com/VanessaE/biome_lib/master/API.txt) included in this package.