docs: add docs for nature module

docs/nature.txt

@@ -0,0 +1,13 @@
+A bit after creation, we have the outside nature. Little plants, seeds,
+growing to their final phase: a full plant. A lot of Hilbish itself is
+written in Go, but there are parts made in Lua, being the `doc` command,
+command not executable/found hooks to print a message in the shell,
+and other things.
+
+Hilbish's Lua core module is called `nature`. It's handled after everything
+on the Go side initializes, which is what that first sentence was from.
+
+# Nature Modules
+Currently, `nature` provides 1 intended public module: `nature.dirs`.
+It is a simple API for managing recent directories and old
+current working directory.