add 18.04 instructions

release-notes/download-archives/2.1.0-preview1-download.md

@@ -22,6 +22,7 @@
 ## Docker
 
 Images for .NET Core 2.1.0-preview1-26216-03 are available on [Docker](https://hub.docker.com/r/microsoft/dotnet/).
+
 ## Installing .NET Core on Linux
 
 ### Uninstall any Preview versions
@@ -34,6 +35,18 @@ If you have .NET Core Previews or daily builds installed, these to be removed be
 
 Register the Microsoft key, the product repository for your distro and install required system dependencies with the following scripts.
 
+#### Ubuntu 18.04
+
+We do not have 18.04 product feeds available yet, there is an option for installing the .NET 2.1 Preview using the Linux binary tar.gz.
+
+First, download [dotnet-sdk-2.1.300-preview1-008174-linux-x64.tar.gz](https://download.microsoft.com/download/D/7/8/D788D3CD-44C4-487D-829B-413E914FB1C3/dotnet-sdk-2.1.300-preview1-008174-linux-x64.tar.gz). Next, run the following commands to unpack the archive and install a needed system dependency.
+
+```bash
+mkdir -p $HOME/dotnet && tar zxf dotnet-sdk-2.1.300-preview1-008174-linux-x64.tar.gz -C $HOME/dotnet
+export PATH=$PATH:$HOME/dotnet
+sudo apt-get install libunwind8
+```
+
 #### Ubuntu 17.10
 
 ```bash