updated README

README.md

@@ -1,10 +1,42 @@
 
 # quickmaths
 
-A small Rust program that can do common math from the command line.
+A small, pretty command line calculator.
 
-I got VERY tired of opening a calculator or a full Python interpreter to do simple math, so I initially created `quickmaths` in Python to do math from the command line.
+Features expression evaluation, variable assignment, an interactive mode, pretty
+output, and a variety of preset constants and functions focused on pure mathematics,
+data science, and computer science.
 
-As the features I wanted changed, such as variable assignment, interactive mode, and output status and formatting, I decided to rebuild the utility in Rust.
+## Constants
+
+|       Name       |  Tokens  |  Type  |        Value        |
+--------------------------------------------------------------
+|  Euler's Number  |   `e`    |   f64  | `2.718281828459045` |
+|   Golden Ratio   |  phi, ϕ  |   f64  | `1.618033988749895` |
+|        Pi        |  pi, π   |   f64  | `3.141592653589793` |
+|     Root Two     |    √2    |   f64  | `1.414213562373095` |
 
 
+## Built-in functions
+
+### Mathematics
+
+- `fix`: fix a float to *n* digits.
+- `log`: logarithm. Defaults to natural logarithm (ln).
+- `sqrt`/`√`: square root. 
+
+### Data Science
+
+- `avg`: average an arbitrary set of numbers.
+
+### Computer Science
+
+- `bin`: convert an integer to a binary string or vice versa.
+- `hex`: convert an integer to a hexadecimal string or vice versa.
+- `oct`: convert an integer to an octal string or vice versa.
+
+## Libraries
+
+- [evalexpr](https://crates.io/crates/evalexpr)
+- [termion](https://crates.io/crates/termion)
+