Update README.md

Author: omid

README.md

@@ -7,12 +7,15 @@
   A parser and evaluator of spreadsheet-like formulas
 </h3>
 
-It's in its early stages, and we are trying to add more functions and features soon.
+Formula is in its early stages and is not ready for production use.
 
 So far we have the following features:
 
 - 18 date time functions
 - 26 text functions
+- 7 logical functions
+- 2 web functions
+- plus all arithmetic and comparison operators
 
 ### Installation and usage
 
@@ -25,18 +28,19 @@ use formula::{Formula, Expr, error::Error};
 use anyhow::Result;
 
 fn main() -> Result<()> {
-    let formula = Formula::new("UPPER(TRIM('   Hello '))")?;
-    let value = formula.parse().unwrap();
+    let formula = Formula::new("=UPPER(TRIM('   Hello '))")?;
+    let value = formula.parse()?;
     assert_eq!(value, Expr::String("HELLO".to_string()));
     Ok(())
 }
 ```
 
-### What we do not support:
+### What we do not support, yet:
 
-- We would like to add more functions, like Excel functions, Google Sheets functions, and more
+- Support of functions are so limited at the moment, but we would like to add more of them, like Excel functions, Google Sheets functions, and so on
 - At the moment, we don't support table data, so you need to pass values to the formula as arguments by yourself
-- We do not support simple formulas like `1+1` or as argument like `AND(1>3, 1<3)` or `SUM(2-1, 2)`, yet
+- We do not support simple formulas like `1+1` or as argument like `AND(1>3, 1<3)` or `SUM(2-1, 2)`. Instead, you can use our `F.` functions like `AND(F.GT(1, 3), F.LT(1, 3))` or `SUM(F.SUB(2, 1), 2)`
+- We still do not support parentheses to change the order of operations, but you can use our `F.` functions. So for example instead of `2*(1+1)`, you should use `F.MUL(2, F.ADD(1, 1))`
 
 ### Contributing
 
@@ -45,3 +49,5 @@ We would love to have your contribution! Please read our [contributing guideline
 ### License
 
 This project is licensed under the MIT license. See the [LICENSE](LICENSE.md) file for more info.
+
+License: MIT