Improve documentation for JSON#parse

Adds information about raised error when fail to parse

ext/json/lib/json/common.rb

@@ -134,6 +134,7 @@ class MissingUnicodeSupport < JSONError; end
   module_function
 
   # Parse the JSON document _source_ into a Ruby data structure and return it.
+  # It raises JSON::ParserError if it fails to parse.
   #
   # _opts_ can have the following
   # keys:
@@ -158,6 +159,7 @@ def parse(source, opts = {})
   # Parse the JSON document _source_ into a Ruby data structure and return it.
   # The bang version of the parse method defaults to the more dangerous values
   # for the _opts_ hash, so be sure only to parse trusted _source_ documents.
+  # It raises JSON::ParserError if it fails to parse.
   #
   # _opts_ can have the following keys:
   # * *max_nesting*: The maximum depth of nesting allowed in the parsed data

ext/json/parser/parser.c

@@ -2098,6 +2098,8 @@ case 9:
  *
  *  Parses the current JSON text _source_ and returns the complete data
  *  structure as a result.
+ *  It raises JSON::ParseError if fail to parse.
+ *
  */
 static VALUE cParser_parse(VALUE self)
 {