Update documentation to show strokes meter and new definition of "word"

Author: arxanas

README.md

@@ -1,17 +1,30 @@
 # About
 
-This is a plugin for Plover to display your typing speed, in words per minute,
-as you type. Words per minute is calculated in one of two ways:
+This is a plugin for Plover to display your typing speed as you type, in either
+or both of words per minute or strokes per minute:
+
+  * **Words per minute**: Shows the rate at which you stroked words in the last
+    10 and 60 seconds.
+  * **Strokes per minute**: Shows how efficiently you stroked words in the last
+    10 and 60 seconds. Lower values are more efficient, e.g. a value of 1 means
+    that on average it took you one stroke to write out a word.
+
+A word is defined in one of three ways:
 
   * **NCRA**: The [National Court Reporters Association](https://www.ncra.org/)
     defines a "word" as 1.4 syllables. This is the measure used for official
     NCRA testing material.
   * **Traditional**: The traditional metric for "word" in the context of
-    keyboarding is defined to be 5 characters per word, including spaces.
+    keyboarding is defined to be 5 characters per word, including spaces. This
+    is compatible with the notion of "word" in many typing speed utilities.
+  * **Spaces**: A word is a whitespace-separated sequence of characters. This
+    metric of course doesn't take into account the fact that some words are
+    longer than others, both in length and syllables.
 
-It looks like this:
+The meters look like this:
 
 ![The WPM meter in action](media/wpm-meter.png)
+![The strokes meter in action](media/strokes-meter.png)
 
 # Installation