NuGet: use new readme format

Author: swharden

src/Spectrogram/README.md

@@ -0,0 +1,36 @@
+**Spectrogram is a .NET library for creating frequency spectrograms from pre-recorded signals, streaming data, or microphone audio from the sound card.**  Spectrogram uses FFT algorithms and window functions provided by the [FftSharp](https://github.com/swharden/FftSharp) project, and it targets .NET Standard so it can be used in .NET Framework and .NET Core projects.
+
+[![](https://raw.githubusercontent.com/swharden/Spectrogram/master/dev/graphics/hal-spectrogram.png)](https://github.com/swharden/Spectrogram)
+
+## Quickstart
+
+```cs
+(double[] audio, int sampleRate) = ReadWavMono("hal.wav");
+var sg = new SpectrogramGenerator(sampleRate, fftSize: 4096, stepSize: 500, maxFreq: 3000);
+sg.Add(audio);
+sg.SaveImage("hal.png");
+```
+
+This example generates the image at the top of the page.
+
+
+## How to Read a WAV File
+
+There are many excellent libraries that read audio files. Consult the documentation _for those libraries_ to learn how to do this well. Here's an example method I use to read audio values from mono WAV files using the NAudio package:
+
+```cs
+(double[] audio, int sampleRate) ReadWavMono(string filePath, double multiplier = 16_000)
+{
+    using var afr = new NAudio.Wave.AudioFileReader(filePath);
+    int sampleRate = afr.WaveFormat.SampleRate;
+    int bytesPerSample = afr.WaveFormat.BitsPerSample / 8;
+    int sampleCount = (int)(afr.Length / bytesPerSample);
+    int channelCount = afr.WaveFormat.Channels;
+    var audio = new List<double>(sampleCount);
+    var buffer = new float[sampleRate * channelCount];
+    int samplesRead = 0;
+    while ((samplesRead = afr.Read(buffer, 0, buffer.Length)) > 0)
+        audio.AddRange(buffer.Take(samplesRead).Select(x => x * multiplier));
+    return (audio.ToArray(), sampleRate);
+}
+```

src/Spectrogram/Spectrogram.csproj

@@ -22,10 +22,8 @@ Release Notes: https://github.com/swharden/Spectrogram/releases</PackageReleaseN
     <PackageReference Include="FftSharp" Version="1.0.8" />
     <PackageReference Include="System.Drawing.Common" Version="5.0.0" />
     <PackageReference Include="runtime.osx.10.10-x64.CoreCompat.System.Drawing" Version="5.8.64" Condition="'$([System.Runtime.InteropServices.RuntimeInformation]::IsOSPlatform($([System.Runtime.InteropServices.OSPlatform]::OSX)))' == 'true'" />
-    <None Include="icon.png">
-      <Pack>True</Pack>
-      <PackagePath></PackagePath>
-    </None>
+    <None Include="icon.png" Pack="true" PackagePath="\" />
+    <None Include="README.md" Pack="true" PackagePath="\" />
   </ItemGroup>
 
 </Project>