Update README.md

Backporting some of the README refinements from nihui/dain-ncnn-vulkan#31.

README.md

@@ -2,27 +2,27 @@
 
 ![CI](https://github.com/nihui/waifu2x-ncnn-vulkan/workflows/CI/badge.svg)
 
-ncnn implementation of waifu2x converter. Runs fast on Intel / AMD / Nvidia with Vulkan API.
+An ncnn implementation of waifu2x converter. Runs fast on Intel / AMD / Nvidia with Vulkan API.
 
 waifu2x-ncnn-vulkan uses [ncnn project](https://github.com/Tencent/ncnn) as the universal neural network inference framework.
 
 ## [Download](https://github.com/nihui/waifu2x-ncnn-vulkan/releases)
 
-Download Windows/Linux/MacOS Executable for Intel/AMD/Nvidia GPU
+Download Windows/Linux/MacOS Executable for Intel/AMD/Nvidia GPUs:
 
 **https://github.com/nihui/waifu2x-ncnn-vulkan/releases**
 
 This package includes all the binaries and models required. It is portable, so no CUDA or Caffe runtime environment is needed :)
 
-## Usages
+## Usage
 
 ### Example Command
 
 ```shell
 waifu2x-ncnn-vulkan.exe -i input.jpg -o output.png -n 2 -s 2
 ```
 
-### Full Usages
+### Full Usage
 
 ```console
 Usage: waifu2x-ncnn-vulkan -i infile -o outfile [options]...
@@ -54,16 +54,20 @@ If you encounter a crash or error, try upgrading your GPU driver:
 - AMD: https://www.amd.com/en/support
 - NVIDIA: https://www.nvidia.com/Download/index.aspx
 
-## Build from Source
+## Building from Source
 
 1. Download and setup the Vulkan SDK from https://vulkan.lunarg.com/
-  - For Linux distributions, you can either get the essential build requirements from package manager
+  - For Linux distributions, you can also get the essential build requirements from your package manager:
+
+Fedora/CentOS/RHEL:
 ```shell
 dnf install vulkan-headers vulkan-loader-devel
 ```
+Debian/Ubuntu
 ```shell
 apt-get install libvulkan-dev
 ```
+Arch/Manjaro
 ```shell
 pacman -S vulkan-headers vulkan-icd-loader
 ```
@@ -174,5 +178,5 @@ waifu2x-ncnn-vulkan.exe -i origin.jpg -o output.png -n 2 -s 2
 
 - https://github.com/Tencent/ncnn for fast neural network inference on ALL PLATFORMS
 - https://github.com/webmproject/libwebp for encoding and decoding Webp images on ALL PLATFORMS
-- https://github.com/nothings/stb for decoding and encoding image on Linux / MacOS
+- https://github.com/nothings/stb for decoding and encoding PNG/JPEG images on Linux / MacOS
 - https://github.com/tronkko/dirent for listing files in directory on Windows