Update 'Arguments'

Arguments.md

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+The glue that holds ARF syntax together is the argument. It is a syntactical
+element that carries a value of any of these types:
+
+- Unsigned integer literal
+- Signed integer literal
+- Float literal
+- String literal
+- Rune literal
+- Identifier
+- Variable definition
+- Phrase with one return value
+
+Any slot in ARF that takes a value is an argument, and can carry these things
+inside of it. The only exception to this is array length initialization, which
+must be an unsigned integer literal.