Add module docstring

fix #15

README.md

@@ -12,7 +12,7 @@
 
 Run `using IPython` and then type `.` in empty `julia>` prompt or run
 `IPython.start_ipython()`.  If you are using IPython 7.0 or above, you
-can switch back to Julia REPl by `backspace` or `ctrl-h` key (like
+can switch back to Julia REPL by `backspace` or `ctrl-h` key (like
 other REPL modes).  For older versions of IPython, exiting IPython as
 usual (e.g., `ctrl-d`) brings you back to the Julia REPL.  Re-entering
 IPython keeps the previous state.  Use pre-defined `Main` object to

src/IPython.jl

@@ -1,3 +1,52 @@
+"""
+Launch IPython in Julia
+
+## Usage
+
+Run `using IPython` and then type `.` in empty `julia>` prompt or run
+`IPython.start_ipython()`.  If you are using IPython 7.0 or above, you
+can switch back to Julia REPL by `backspace` or `ctrl-h` key (like
+other REPL modes).  For older versions of IPython, exiting IPython as
+usual (e.g., `ctrl-d`) brings you back to the Julia REPL.  Re-entering
+IPython keeps the previous state.  Use pre-defined `Main` object to
+access Julia namespace from IPython.  Use `py"..."` string macro to
+access Python namespace from Julia.
+
+**Note:**
+First launch of IPython may be slow.
+
+# Examples
+```
+julia> xs = [1, 2, 3];  # some Julia variable
+
+julia> using IPython
+
+julia> IPython.start_ipython()  # or type . (a dot)
+
+In [1]: Main.xs  # accessing Julia variable
+array([1, 2, 3], dtype=int64)
+
+In [2]: Main.xs += 10
+
+In [3]: ε = "varepsilon"
+
+In [4]: exit()  # or type backspace or ctrl-d
+
+julia> xs
+3-element Array{Int64,1}:
+ 11
+ 12
+ 13
+
+julia> using PyCall
+
+julia> py"ε"  # you can access Python variables with PyCall.@py_str macro
+"varepsilon"
+
+julia> py"ϵ"  # but be careful when using Unicode!
+"varepsilon"
+```
+"""
 module IPython
 
 using Compat