docs: add notes about DS, usage and features

Author: anshumanv

.gitignore

@@ -1,2 +1,4 @@
 node_modules
 dist
+coverage
+styleguide

README.md

@@ -58,16 +58,27 @@ const validationFn = val => {
 
 <ExpressionBuilder
   onChangeFn={onChangeFn}
-  expressionRootClass={expressionRootClass}
-  expressionInputClass={expressionInputClass}
   options={options}
-  placeholder="Enter your expression"
+  expressionRootClass={expressionRootClass} // Optional
+  expressionInputClass={expressionInputClass} // Optional
+  placeholder="Enter your expression" // Optional
   initialFocus={true} // if you want your input to be focussed on mount by default
-  validationFn={validationFn}
+  validationFn={validationFn} // Optional
 />
 
 ```
 
+### Features
+
+- Typeahead support
+- Full keyboard navigation and deletion
+- Easy custom styling as per input
+- Input validation at granular level
+
+### Data Structure
+
+Uses an N-Ary tree to contain the expression data, simple recursive function gives you the complete string. Y
+
 ## Author
 
 [Anshuman Verma](https://github.com/anshumanv)

src/Test.tsx

@@ -9,7 +9,7 @@ const stringRegex = /"([^\\"]|\\")*"/
 const cb1 = () => alert('valid!')
 const cb2 = () => alert('invalid!')
 
-const onChangeFn = st => console.log('change', st)
+const onChangeFn = st => console.log('change', st.buildExpression())
 const expressionRootClass = 'root-class'
 const expressionInputClass = 'input-class'