README.md in cousin_roman-1.0.4 vs README.md in cousin_roman-1.0.5

@@ -1,11 +1,25 @@
 # CousinRoman
 
-`CousinRoman` provides functionality to convert between Roman and Arabian numerals.
-
+CousinRoman provides functionality to convert between Roman and Arabian numerals.
 The functionality provided via String and Integer extensions.
 
+## Roman numbers and conversion rules
+
+CousinRoman follows strict roman notation with subtractive rule, i.e.
+
+1. Letters should be ordered by decreasing of magnitude.
+2. Only I, X, C, M can be repeated, but up to three times.
+3. Letter with lower magnitude can appear BEFORE letter with higher magnitude,
+but only in the following cases: IV, IX, XL, XC, CD, CM - lets call them **subtractives**
+4. **subtractives** and regular letters cannot appear within the same power,
+i.e. `ivi` is not allowed.
+
+Therefore, only numbers within range of 1..3999 can be represented in roman notation.
+
+CousinRoman is thoroughly spec'ed, and considered reliable in following these rules.
+
 ## Installation
 
 Add this line to your application's Gemfile:
 
     gem 'cousin_roman'
@@ -35,9 +49,13 @@
 
 2013.to_roman # => 'MMXIII'
 '0'.to_roman # => nil
 '100500'.to_roman! # => TypeError: not a valid roman number
 ```
+
+`String#to_arabian(!)` is case insensitive.
+
+`Integer#to_roman(!)` returns numerals in upper case.
 
 ## Testing
 
 Just run