Format symbol-value table in readme

Updated the readme to format the symbol-value table for better readability.

Author: javadev

src/main/java/g0001_0100/s0013_roman_to_integer/readme.md

@@ -4,7 +4,15 @@ Easy
 
 Roman numerals are represented by seven different symbols: `I`, `V`, `X`, `L`, `C`, `D` and `M`.
 
-**Symbol** **Value** I 1 V 5 X 10 L 50 C 100 D 500 M 1000
+| Symbol | Value |
+|--------|-------|
+| I | 1 |
+| V | 5 |
+| X | 10 |
+| L | 50 |
+| C | 100 |
+| D | 500 |
+| M | 1000 |
 
 For example, `2` is written as `II` in Roman numeral, just two ones added together. `12` is written as `XII`, which is simply `X + II`. The number `27` is written as `XXVII`, which is `XX + V + II`.
 
@@ -44,4 +52,4 @@ Given a roman numeral, convert it to an integer.
 
 *   `1 <= s.length <= 15`
 *   `s` contains only the characters `('I', 'V', 'X', 'L', 'C', 'D', 'M')`.
-*   It is **guaranteed** that `s` is a valid roman numeral in the range `[1, 3999]`.
+*   It is **guaranteed** that `s` is a valid roman numeral in the range `[1, 3999]`.