Add documentation for versioning policy going forward (#542)

Author: John Luo

doc/images/packages.png

@@ -0,0 +1,32 @@
+# gRPC-dotnet package versioning policies
+
+## Overview
+
+This document covers versioning policies of the packages produced in this repo:
+
+- Grpc.AspNetCore
+- Grpc.AspNetCore.Server
+- Grpc.AspNetCore.Server.ClientFactory
+- Grpc.Net.Client
+- Grpc.Net.ClientFactory
+- Grpc.Net.Common
+- dotnet-grpc
+
+## Design considerations
+
+### Major version number
+
+The initial major version number was set to 2 to match the release of corresponding Grpc.Core packages. Going forward, the major version will be incremented when there's a need to ingest a major Grpc.Core or ASP.NET Core dependency for breaking changes. grpc-dotnet complies with the gRPC-wide [versioning policy](https://github.com/grpc/grpc/blob/master/doc/versioning.md) and the major version will only be incremented on rare occasions.
+
+### Minor version number
+
+The initial minor version number was set to 23 to match the release of corresponding Grpc.Core packages. Going forward, we will be releasing on the Grpc.Core [schedule](https://github.com/grpc/grpc/blob/master/doc/grpc_release_schedule.md) and will match the minor version number of the corresponding release.
+
+### Patch version number
+
+The patch number will increment for patches of existing major.minor release. These patches are built out of the v{major}.{minor}.x branches on GitHub, e.g. https://github.com/grpc/grpc-dotnet/tree/v2.23.x.
+
+## Pre-release and nightly suffixes
+
+The suffix -pre{x} will be added to pre-release packages released to nuget.org. These are non-stable packages intended for early ingestion of upcoming releases.
+The suffix -dev is added to packages produced by nightly builds available from the NuGet feed https://grpc.jfrog.io/grpc/api/nuget/v3/grpc-nuget-dev.

doc/versioning.md

@@ -7,7 +7,7 @@
     <IsGrpcPublishedPackage>true</IsGrpcPublishedPackage>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <TargetFramework>netcoreapp3.0</TargetFramework>
-    
+
     <!-- Disable analysis for ConfigureAwait(false) -->
     <WarningsNotAsErrors>$(WarningsNotAsErrors);CA2007</WarningsNotAsErrors>
     <NoWarn>$(NoWarn);CA2007</NoWarn>
@@ -22,7 +22,7 @@
     <FrameworkReference Include="Microsoft.AspNetCore.App" />
 
     <ProjectReference Include="..\Grpc.Net.Common\Grpc.Net.Common.csproj" />
-    
+
     <PackageReference Include="Grpc.Core.Api" Version="$(GrpcPackageVersion)" />
   </ItemGroup>