Added a module docstring

Author: jwodder

README.md

@@ -20,8 +20,8 @@ Requirements
 * bash
 
 
-Installation
-============
+Installation & Usage
+====================
 
 1. Save [`ps1.py`](ps1.py) to your computer somewhere (I put my copy at
    `~/share/ps1.py`)
@@ -30,7 +30,8 @@ Installation
 
         PROMPT_COMMAND="$PROMPT_COMMAND"'; PS1="$(/usr/bin/python3 ~/share/ps1.py "${PS1_GIT:-}")"'
 
-    Replace `~/share/ps1.py` with the location you saved `ps1.py` at as
+    Replace `/usr/bin/python3` with the path to your Python 3 interpreter, and
+    replace `~/share/ps1.py` with the location you saved `ps1.py` at as
     appropriate.
 
 3. Open a new shell
@@ -39,7 +40,7 @@ Installation
 
 5. If the Git integration causes you trouble (either because something breaks
    or just because it's taking too long to run), it can be temporarily disabled
-   by setting `PS1_GIT=off` in bash.
+   by running `PS1_GIT=off` in bash.
 
 
 Git Status Symbols
@@ -62,7 +63,7 @@ relevant.  From left to right, the symbols are:
   working tree:
     - Green: There are staged changes
     - Red: There are unstaged changes
-    - Light yellow: There are both staged and unstaged changes
+    - Bold light yellow: There are both staged and unstaged changes
 - `+` (bold red) — Indicates there are untracked files in the working tree
 - `[STATE]` (magenta) — Shows what activity Git is currently in the middle of,
   if any:

ps1.py

@@ -1,4 +1,44 @@
 #!/usr/bin/python3
+"""
+Yet another bash prompt script
+
+Here we have yet another script for Git-aware customization of the bash command
+prompt.  Unlike all the other scripts, I wrote this one, so it's better.
+
+Features:
+
+- lets you know if you have mail in ``$MAIL``
+- shows chroot and `virtualenv <https://virtualenv.pypa.io>`_ prompt prefixes
+- automatically truncates the current directory path if it gets too long
+- shows the status of the current Git repository (see below)
+- thoroughly documented and easily customizable
+
+Visit <https://github.com/jwodder/ps1.py> for more information.
+
+
+Installation & Usage
+====================
+
+1. Save this script to your computer somewhere (I put my copy at
+   ``~/share/ps1.py``)
+
+2. Add the following line to the end of your ``~/.bashrc``::
+
+        PROMPT_COMMAND="$PROMPT_COMMAND"'; PS1="$(/usr/bin/python3 ~/share/ps1.py "${PS1_GIT:-}")"'
+
+    Replace ``/usr/bin/python3`` with the path to your Python 3 interpreter,
+    and replace ``~/share/ps1.py`` with the location you saved ``ps1.py`` at as
+    appropriate.
+
+3. Open a new shell
+
+4. Enjoy!
+
+5. If the Git integration causes you trouble (either because something breaks
+   or just because it's taking too long to run), it can be temporarily disabled
+   by running ``PS1_GIT=off`` in bash.
+"""
+
 from   enum       import Enum
 import os
 from   pathlib    import Path, PurePath