Converted README to markdown format and added screenshot.

README.markdown

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+Many modern editors and IDEs can graphically indicate the location of the
+fill column by drawing a thin line (in design parlance, a `rule') down the
+length of the editing window.  Fill-column-indicator implements this
+facility in Emacs:
+
+![](./FciRuleStyle.png)
+
+Installation and Usage
+======================
+
+Put this file in your load path and put
+
+  (require 'fill-column-indicator)
+
+in your .emacs.
+
+To toggle graphical indication of the fill column in a buffer, use the
+command `fci-mode'.
+
+Configuration
+=============
+
+The color of the fill-column rule is controlled by the variable
+`fci-rule-color'.  Its value can be any valid color name.  If nil (the
+default value), fci-mode tries to select an appropriate color
+automatically.
+
+On graphical displays, the rule is drawn using a bitmap image generated by
+fci-mode.  The rule's width (in pixels) is determined by the variable
+`fci-rule-width'.  The default value is 2.
+
+On character terminals the rule is drawn using the character specified by
+`fci-rule-character'; the default is `|' (ascii 124).  If you'd like the
+rule to be drawn using fci-rule-character even on graphical displays, set
+`fci-always-use-textual-rule' to a non-nil value.
+
+The image formats used by fci-mode are XPM, PBM, and XBM.  By default, it
+uses XPM images if Emacs has been compiled with the appropriate library;
+if not, it uses PBM images, which are natively supported.  You can specify
+a particular format by setting `fci-rule-image-format' to either 'xpm,
+'xpm, or 'xbm.
+
+Other Options
+=============
+
+When `truncate-lines' is nil, the effect of drawing a fill-column
+indicator is very odd looking. Indeed, in a window with continuation
+lines, it makes little sense to indicate the position of the fill column
+relative to the window edge (think about what it would mean to talk about
+"the" location of the fill column in that case).  For this reason,
+fci-mode sets truncate-lines to t in buffers in which it is enabled and
+restores it to its previous value when disabled.  You can turn this
+feature off by setting `fci-handle-truncate-lines' to nil.
+
+If `line-move-visual' is t, then vertical navigation can behave oddly in
+several edge cases while fci-mode is enabled (this is due to a bug in C
+code).  Accordingly, fci-mode locally sets line-move-visual to nil when
+enabled and restores it when disabled.  This can be suppressed by setting
+`fci-handle-line-move-visual' to nil.  (But you shouldn't want to do
+this.  There's no reason to use line-move-visual if truncate-lines is t,
+and it doesn't make sense to use something like fci-mode when
+truncate-lines is nil.)
+
+Troubleshooting
+===============
+
+o If the fill-column rule is misaligned on some lines but otherwise looks
+  normal, then you're most likely not displaying the buffer contents with
+  a monospaced font.  Check whether the lines in question contain
+  non-ascii characters that are wider or shorter than the normal character
+  width.  Also, be aware that certain font-lock themes set some faces so
+  that they look monospaced but aren't quite so.
+
+o Although the XBM format is natively supported by Emacs, the
+  implementation on some ports is incomplete; the v23 and v24 Mac OS X
+  ports are examples.  On these systems XBM images are always drawn in
+  black, in which case one cannot control the color of the rule.  Use XPM
+  or PBM images instead.
+
+o Fci-mode needs free use of two characters (specifically, it needs the
+  use of two characters whose display table entries it can change
+  arbitrarily).  By default, it uses the first two characters of the
+  Private Use Area of the Unicode BMP, viz. U+E000 and U+E001.  If you
+  need to use those characters for some reason, set `fci-padding-char' and
+  `fci-eol-char' to different values.
+
+Known Issues
+============
+
+o The indicator extends only to end of the buffer contents (as opposed to
+  running the full length of the editing window).
+
+o When portions of a buffer are invisible, such as when outline mode is
+  used to hide certain lines, the fill-column rule is hidden as
+  well.  (Working around this would require either (a) rewriting a large
+  part of xdisp.c, or (b) advising every function that might hide part of
+  a buffer.)
+
+o Fci-mode is generally fast:  Displaying the rule should be O(n) in the
+  number of lines in a buffer, with a low constant.  (Activating the mode
+  in a buffer with 30k lines should take under 0.5 sec on a modern
+  machine.)  However, the presence of multibyte characters can slow down
+  its performance, in proportion to the number of multibyte characters in
+  the buffer.  (This problem stems from the fact that the performance of
+  the primitive overlay commands is degraded by multibyte characters.)
+
+o An issue specifc to the Mac OS X (NextStep) port, versions 23.0-23.2: On
+  graphical displays, the cursor will disappear when positioned directly
+  on top of the fill-column rule (i.e., when it is positioned at the end
+  of a line that extends up to but not past the fill-column).  The best
+  way to deal with this is to upgrade to 23.3 or to 24 (or downgrade to
+  22).  If that isn't practical, a fix is available via the mini-package
+  fci-osx-23-fix.el, which can be downloaded from either:
+
+    github.com/alpaker/Fill-Column-Indicator
+
+  or
+
+    emacswiki.org/emacs/FillColumnIndicator
+
+ Directions for its use are given in the file header.
+
+Todo
+====
+
+Accomodate non-nil values of `hl-line-sticky-flag' and similar cases.
+