Improved readme

readme.md

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 # avr-fast-div: optimized integer division for AVR hardware
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 This library provides *up to* 60% improvement in run time division speed on AVR hardware. Exact speedup varies depending on data types & number ranges - see below for details (also see the [unit tests](https://github.com/adbancroft/avr-fast-div/actions/workflows/unit-tests.yml)).
 
 As a general guideline, avr-fast-div is applicable to these operations:
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 ### Constraints
 1. division using a signed type and unsigned type is not supported. E.g. `int16_t/uint16_t` (it's also a recipe for confusion, since C++ converts the signed integer to an unsigned one before doing the division).
 2. There is no 64-bit support
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 ## Using the library
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 ### Installation
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 The library is available in both the [Arduino Library](https://www.arduino.cc/reference/en/libraries/avr-fast-div/) and [PlatformIO Library](https://registry.platformio.org/libraries/adbancroft/avr-fast-div) registries. 
 
 The library can also be cloned & included locally or included directly from GitHub (if your tooling supports it). 
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 ### Code
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 1. `#include <avr-fast-div.h>`
 2. Replace divide operations with a call to fast_div. I.e.
     * `a / b` -> `fast_div(a, b)`
@@ -35,7 +44,9 @@ The code base is compatible with all platforms: non-AVR builds compile down to t
 **Note:** if the divisor (`b`) is a [compile time constant greater than 8-bits](https://stackoverflow.com/questions/47994933/why-doesnt-gcc-or-clang-on-arm-use-division-by-invariant-integers-using-multip), you probably want to use [libdivide](https://libdivide.com/) instead.
 
 You can reduce the amount of flash (.text segment) the library uses by defining `AFD_SMALL_TEXT`: this will reduce performance by up to 5% in some cases.
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 ## Details
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 Since the AVR architecture has no hardware divider, all run time division is done in software by the compiler emitting a call to one of the division functions (E.g. [__udivmodsi4](https://github.com/gcc-mirror/gcc/blob/cdd5dd2125ca850aa8599f76bed02509590541ef/libgcc/config/avr/lib1funcs.S#L1615)) contained in a [runtime support library](https://gcc.gnu.org/wiki/avr-gcc#Exceptions_to_the_Calling_Convention).
 
 By neccesity, the division functions are optimised for the general case. Combined with integer type promotion, this can result in sub-optimal division speed. E.g.