Use BigDecimal in devguide (#221)

docs/DeveloperGuide.md

@@ -17,6 +17,8 @@ _{ list here sources of all reused/adapted ideas, code, documentation, and third
 
 1. CS2103T AB3 Source Code
 2. https://uibakery.io/regex-library/phone-number-java - Regarding Phone Validation Java Regex
+3. Java documentation for BigDecimal https://docs.oracle.com/javase/8/docs/api/java/math/BigDecimal.html.
+
 --------------------------------------------------------------------------------------------------------------------
 
 ## **Setting up, getting started**
@@ -280,8 +282,8 @@ CCA members. An example command is ``split a/4.00 c/NUS Cycling``. Which means
 
 1. Identify all members belonging to that CCA.
 2. Count the number of members in 1., and split the amount equally.
-   * Note: rounding errors may occur here. So we should use `double` in Java
-     for higher precision and also round to nearest 2 d.p.
+   * Note: rounding errors may occur here. So we should use `BigDecimal` in Java
+     for higher precision.
 3. Add the split amount to each member's "payment owed" field