Flesh out the readme a bit more.

README.md

@@ -1,6 +1,6 @@
 # SallyForth: A simple Forth-like language implemented in Python.
 
-SallyForth is a simple hobby implementation of the FORTH programming
+SallyForth is a simple hobby implementation of a FORTH-like programming
 language. Possibly the most interesting thing about SallyForth is the
 name, which 
 [Michael Nygard suggested](https://twitter.com/mtnygard/status/1249781530219642883)
@@ -16,3 +16,91 @@ run SallyForth just kick off the sallyforth.py file:
 ````
 $ python sallyforth/sallyforth.py
 ````
+
+## The Sally Language
+
+Like FORTH, Sally is a stack oriented concatenative programming language.
+What this means is that any constant value in a sallyforth program,
+like a number or a string:
+
+```
+sallySh> "Hello, world!"
+```
+
+Has the effect of pushing the value onto an ever present data stack.
+There are also commands or functions -- called *words* -- that you
+can use to do things.
+
+So the word `p` will pop the value off of the top of the stack 
+and print it:
+
+
+```
+sallySh> "Hello, world!"
+sallySh> p
+Hello, world!
+```
+
+Sally parsing is about as simple as you can get: words and constant
+values are separated by whitespace. So if you wanted to print
+a number of values, you could do this:
+
+```
+sallySh> 1 2 3 p p p
+3
+2
+1
+```
+
+The only execeptions to the _separated by whitespace rule_ are
+double quoted strings, which work about the way you would expect:
+
+```
+sallySh> "I can have spaces in my string"
+sallySh> p
+I can have spaces in my string
+```
+
+Sally comes prepackaged with a host of useful words, everything
+from basic arithmetic:
+
+```
+sallySh> 1 2 + p
+3
+sallySh> 10 10 * 1 + p
+101
+```
+
+To boolean logic:
+
+sallySh> true false and p
+False
+sallySh> false true or p
+True
+
+To IO:
+
+```
+sallySh> "hello.txt" read-file
+sallySh> p
+This is the contents of hello.txt.
+Use it wisely.
+```
+
+You can also define your own words. A word defintion starts with
+a colon, followed by the name of your new word, followed by
+the contents of your new word, followed by a semicolon. 
+Keep in mind that everything -- including the colon and semicolon,
+needs to be set off with whitespace:
+
+```
+: hello-world "Hello, world!" p ;
+```
+
+Once your new word is defined you can use it like any other word:
+
+```
+sallySh> hello-world
+Hello, world!
+```
+