update readme

Author: ablaom

README.md

@@ -3,77 +3,74 @@
 [![Build Status](https://github.com/JuliaAI/MLJModels.jl/workflows/CI/badge.svg)](https://github.com/JuliaAI/MLJModels.jl/actions)
 [![codecov](https://codecov.io/gh/JuliaAI/MLJModels.jl/graph/badge.svg?token=KgarnnCc0K)](https://codecov.io/gh/JuliaAI/MLJModels.jl)
 
-Repository of the "built-in" models available for use in the
-[MLJ](https://github.com/JuliaAI/MLJ.jl) MLJ machine
-learning framework; and the home of the MLJ model registry.
+Home of the [MLJ](https://juliaml.ai) Model Registry and tools for model search and model code loading. 
 
-For instructions on integrating a new model with MLJ visit
-[here](https://JuliaAI.github.io/MLJ.jl/dev/adding_models_for_general_use/)
+For instructions on integrating a new model into MLJ visit
+[here](https://juliaai.github.io/MLJModelInterface.jl/stable/).
 
 
 ### Contents
 
  - [Who is this repo for?](#who-is-this-repo-for)
+ - [How to register new models](#how-to-register-new-models)
  - [What is provided here?](#what-is-provided-here)
- - [Instructions for updating the MLJ model registry](#instructions-for-updating-the-mlj-model-registry)
 
 ## Who is this repo for?
 
-General users of the MLJ machine learning platform should refer to
-[MLJ home page](https://JuliaAI.github.io/MLJ.jl/dev/)
-for usage and installation instructions. MLJModels is a dependency of
-MLJ that the general user can ignore.
+Newcomers to MLJ should refer to [this page](https://juliaml.ai) for usage and
+installation instructions. MLJModels.jl is a dependency of MLJ that the general user can
+ignore.
 
-This repository is for developers wishing to
-[register](#instructions-for-updating-the-mlj-model-registry) new MLJ
-model interfaces, whether they be:
+This repository is for developers maintaining:
 
-- implemented **natively** in a
-  package providing the core machine learning algorithm, as in
+- The [MLJ Model Registry](/src/registry), a database of packages implementing the MLJ
+  interface for machine learning models, together with metadata about those models.
+
+- MLJ tools for searching the database (`models(...)` and `matching(...)`) and for loading
+  model code (`@load`, `@iload`).
+
+## How to register new models
+
+The model registry lives at "/src/registry" but
+is maintained using
+[MLJModelRegistryTools.jl](https://juliaai.github.io/MLJModelRegistryTools.jl/dev/).
+
+New MLJ model interfaces can be implemented either:
+
+- **natively** in a package providing the core machine learning algorithm, as in
   [`EvoTrees.jl`](https://github.com/Evovest/EvoTrees.jl/blob/master/src/MLJ.jl); or
 
-- implemented in a separate **interface package**, such as
+-  in a separate **interface package**, such as
   [MLJDecisionTreeInterface.jl](https://github.com/JuliaAI/MLJDecisionTreeInterface.jl).
 
-It also a place for developers to add models (mostly transformers)
-such as `OneHotEncoder`, that are exported for "built-in" use in
-MLJ. (In the future these models may live in a separate package.)
-
-To list *all* model interfaces currently registered, do `using MLJ` or
-`using MLJModels` and run:
+In either case, the package providing the implementation needs to be added to the MLJ
+Model Registry to make it discoverable by MLJ users, and to make the model metadata
+searchable. To register a package, prepare a pull request to MLJModels.jl by following [these instructions](https://juliaai.github.io/MLJModelRegistryTools.jl/dev/registry_management_tools/#Registry-management-tools).
 
-- `localmodels()` to list built-in models (updated when external models are loaded with `@load`)
+Currently, after registering the model, one must also make a PR to MLJ updating [this
+dictionary of model
+descriptors](https://github.com/JuliaAI/MLJ.jl/blob/dev/docs/ModelDescriptors.toml) to
+ensure the new models appear in the right places in MLJ's [Model
+Browser](https://JuliaAI.github.io/MLJ.jl/dev/model_browser/#Model-Browser)
 
-- `models()` to list all registered models, or see [this list](/src/registry/Models.toml).
+To list *all* model interfaces currently registered, do `using MLJ` or `using MLJModels`
+and run `models()` to list all registered models.
 
 Recall that an interface is loaded from within MLJ, together with the
 package providing the underlying algorithm, using the syntax `@load
 RidgeRegressor pkg=GLM`, where the `pkg` keyword is only necessary in
 ambiguous cases.
 
-
 ## What is provided here?
 
-MLJModels contains:
-
-- transformers to be pre-loaded into MLJ, located at
-  [/src/builtins](/src/builtins), such as `OneHotEncoder`
-  and `ConstantClassifier`. 
-
-- the MLJ [model registry](src/registry/Metadata.toml), listing all
-  models that can be called from MLJ using `@load`. Package developers
-  can register new models by implementing the MLJ interface in their
-  package and following [these
-  instructions](https://JuliaAI.github.io/MLJ.jl/dev/adding_models_for_general_use/).
-  
-
-## Instructions for updating the MLJ model registry
+The actual MLJ Model Registry consists of the TOML files in [this
+directory](/src/registry). A few models available for immediate use in MLJ (without
+loading model code using `@load`) are also provided by this package, under "/src/builtins"
+but these may be moved out in the future.
 
-Generally model registration is performed by administrators. If you
-have an interface you would like registered, open an issue
-[here](https://github.com/JuliaAI/MLJ.jl/issues). 
+### Historical note
 
-**Administrator instructions.** These are given in the
-`MLJModels.@update` document string. After registering the model, make a PR to MLJ 
-updating [this dictionary of model descriptors](https://github.com/JuliaAI/MLJ.jl/blob/dev/docs/ModelDescriptors.toml) 
-to ensure the new models appear in the right places in MLJ's [Model Browser](https://JuliaAI.github.io/MLJ.jl/dev/model_browser/#Model-Browser)
+Older versions of MLJModels.jl contained some of the models now residing at
+[MLJTransforms.jl](https://github.com/JuliaAI/MLJTransforms.jl/tree/dev). Even older
+versions provided implementations of all the non-native implementations of the
+MLJ interface.