Add a basic README

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Author: omus

README.md

@@ -4,3 +4,44 @@
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+
+Provides the fixed-point decimal type `FixedDecimal` allowing for exact representations of
+decimal numbers. These numbers are useful in financial calculations where interactions
+between decimal numbers are required to be exact.
+
+This library defines the type `FixedDecimal{T <: Integer, f}` as a subtype of `Real`. The
+parameter `T` is the underlying machine representation and `f` is the number of decimal
+places which can be stored.
+
+For example, `FixedDecimal{Int8, 2}` allows you to a decimal number with up to 2 fractional
+digits. All `FixedDecimal{Int8, 2}` numbers `x` must satisfy
+
+```
+-1.28 = -128/10² ≤ x ≤ 127/10² = 1.27
+```
+
+because the range of `Int8` is from -128 to 127.
+
+In general `FixedDecimal{T <: Integer, f}` numbers `y` must satisfy:
+
+```
+typemin(T)/10ᶠ ≤ y ≤ typemax(T)/10ᶠ
+```
+
+## Usage
+
+```julia
+julia> using FixedPointDecimals
+
+julia> 2.2 / 10
+0.22000000000000003
+
+julia> FixedDecimal{Int,2}(2.2) / 10
+FixedDecimal{Int64,2}(0.22)
+
+julia> 0.1 + 0.2
+0.30000000000000004
+
+julia> FixedDecimal{Int,1}(0.1) + FixedDecimal{Int,1}(0.2)
+FixedDecimal{Int64,1}(0.3)
+```