docs: Added new version update instructions

[Anush008]

As the title goes

[russcam]

The build exe that this invokes only downloads files from a given <QdrantVersion> once

qdrant-dotnet/build/Main.cs

Lines 56 to 60 in e30739f

	if (Directory.Exists(protosTagDir) && Directory.EnumerateFileSystemEntries(protosTagDir).Any())
	{
	Console.WriteLine($"Already downloaded protos for {qdrantVersion}");
	return;
	}

For a constantly changing upstream branch like dev, may want to either

• introduce a command line argument to delete the downloaded proto files

or

• introduce a convention to delete downloaded proto files for given <QdrantVersion>s

[Anush008]

Thanks.
Added a new flag.
3c334be (#69)