refactor(src/emacs/README.md): clarify setup instructions

src/emacs/README.md

@@ -42,8 +42,27 @@ installation instructions below.
 Installation
 ============
 
-Put the following elisp code in your emacs setup
-(e.g. ``.emacs.d/init.el`` [GNU Emacs], ``~/Library/Preferences/Aquamacs Emacs/Preferences.el`` [Aquamacs]) :
+When Emacs is started, it loads startup information from a special
+initialization file, often called an "init file." The init file can be
+found in different places on different systems:
+
+- Emacs will check for a file named ``.emacs`` in your home directory.
+- With GNU Emacs, it is common to use ``.emacs.d/init.el`` instead.
+- With Aquamacs, it is common to use ``~/Library/Preferences/Aquamacs Emacs/Preferences.el``.
+
+On Windows, there are two additional complications: 
+
+- It may be hard to figure out what Emacs considers to be your "home
+  directory".
+- The file explorer may not let you create a file named ``.emacs``,
+  since it begins with a period.
+
+One solution is to run Emacs itself and create the file using C-c C-f
+(control-C, control-F) and then entering ``~/.emacs``. (The tilde
+indicates your home directory.) On Windows, you can also name the file
+``_emacs``.
+ 
+Put the following code in your Emacs init file:
 
 ```elisp
 (require 'package)
@@ -66,7 +85,8 @@ Put the following elisp code in your emacs setup
       (package-install p))))
 ```
 
-Please choose your installation method from the following scenarios, and add the elisp code to your emacs setup:
+Then choose your installation method from the following scenarios, and
+add the corresponding code to your init file:
 
 Case 1: Build Lean from source
 -----------------------------