Add README.md

README.md

@@ -2,6 +2,53 @@
 
 [![Stable](https://img.shields.io/badge/docs-stable-blue.svg)](https://tkf.github.io/IndirectImports.jl/stable)
 [![Dev](https://img.shields.io/badge/docs-dev-blue.svg)](https://tkf.github.io/IndirectImports.jl/dev)
+![GitHub commits since tagged version](https://img.shields.io/github/commits-since/tkf/IndirectImports.jl/v0.1.1.svg)
 [![Build Status](https://travis-ci.com/tkf/IndirectImports.jl.svg?branch=master)](https://travis-ci.com/tkf/IndirectImports.jl)
 [![Codecov](https://codecov.io/gh/tkf/IndirectImports.jl/branch/master/graph/badge.svg)](https://codecov.io/gh/tkf/IndirectImports.jl)
 [![Coveralls](https://coveralls.io/repos/github/tkf/IndirectImports.jl/badge.svg?branch=master)](https://coveralls.io/github/tkf/IndirectImports.jl?branch=master)
+
+IndirectImports.jl lets Julia packages call and extend (a special type
+of) functions without importing the package defining them.  This is
+useful for managing optional dependencies.
+
+* Compared to Requires.jl, IndirectImports.jl's approach is more
+  static and there is no run-time `eval` hence more compiler friendly.
+  However, unlike Requires.jl, both upstream and downstream packages
+  need to rely on IndirectImports.jl API.
+
+* Compared to "XBase.jl" approach, IndirectImports.jl is more flexible
+  in the sense that you don't need to create an extra package and keep
+  it in sync with the "implementation" package(s).  However, unlike
+  "XBase.jl" approach, IndirectImports.jl is usable only for
+  functions, not for types.
+
+## Example
+
+```julia
+# MyPlot/src/MyPlot.jl
+module MyPlot
+    using IndirectImports
+
+    @indirect function plot end  # declare an "indirect function"
+
+    @indirect function plot(x)  # optional
+        # generic implementation
+    end
+end
+
+# MyDataFrames/src/MyDataFrames.jl
+module MyDataFrames
+    using IndirectImports
+
+    @indirect import MyPlot  # this does not actually load MyPlot.jl
+
+    # you can extend indirect functions
+    @indirect function MyPlot.plot(df::MyDataFrame)
+        # you can call indirect functions
+        MyPlot.plot(df.columns)
+    end
+end
+```
+
+You can install it with `]add IndirectImports`.  See more details in
+the [documentation](https://tkf.github.io/IndirectImports.jl/dev/).

src/IndirectImports.jl

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+@doc read(joinpath(dirname(@__DIR__), "README.md"), String) ->
 module IndirectImports
 
 export @indirect