Add initial docs

Author: Havret

README.md

@@ -1 +1,33 @@
-# System.Text.Json.Protobuf
+# System.Text.Json.Protobuf
+
+This library provides support for Protobuf types to [System.Text.Json](https://www.nuget.org/packages/System.Text.Json/).
+
+## Performance
+
+``` ini
+BenchmarkDotNet=v0.13.1, OS=macOS Monterey 12.3 (21E230) [Darwin 21.4.0]
+Apple M1 Pro, 1 CPU, 10 logical and 10 physical cores
+.NET SDK=6.0.101
+  [Host]     : .NET 6.0.1 (6.0.121.56705), Arm64 RyuJIT
+  DefaultJob : .NET 6.0.1 (6.0.121.56705), Arm64 RyuJIT
+```
+
+### Simple message
+|                                       Method |      Mean |     Error |    StdDev |
+|--------------------------------------------- |----------:|----------:|----------:|
+|                SystemTextJsonProtobufSupport |  2.572 μs | 0.0094 μs | 0.0074 μs |
+| NewtonsoftJsonWithProtobufParserAndFormatter | 17.250 μs | 0.1492 μs | 0.1395 μs |
+
+
+### Message with oneofs
+|                                       Method |      Mean |     Error |    StdDev |
+|--------------------------------------------- |----------:|----------:|----------:|
+|                SystemTextJsonProtobufSupport |  3.115 μs | 0.0065 μs | 0.0057 μs |
+| NewtonsoftJsonWithProtobufParserAndFormatter | 18.384 μs | 0.0403 μs | 0.0377 μs |
+
+
+### Message with repeated fields
+|                                       Method |     Mean |   Error |  StdDev |
+|--------------------------------------------- |---------:|--------:|--------:|
+|                SystemTextJsonProtobufSupport | 100.9 μs | 0.19 μs | 0.17 μs |
+| NewtonsoftJsonWithProtobufParserAndFormatter | 735.1 μs | 1.09 μs | 1.02 μs |