Update onboarding documentation to note that long repository root pat…

…hs can cause build failures (#2551)

sln/OData.E2E.md

@@ -2,7 +2,7 @@
 2. Install [.NET Core SDK 1.1.14](https://dotnet.microsoft.com/download/dotnet/1.1)
 3. Install [.NET Core SDK 2.1.818](https://dotnet.microsoft.com/download/dotnet/2.1)
 4. Despite being documented as included in .NET Core SDK 2.1.818, install [.NET Core Runtime 2.1.30](https://dotnet.microsoft.com/download/dotnet/2.1)
-5. Create a local directory for the repository, then run `git clone https://github.com/OData/odata.net.git` from the command prompt in that directory
+5. Create a local directory for the repository, then run `git clone https://github.com/OData/odata.net.git` from the command prompt in that directory. NOTE: A build issue currently exists which generates extremely long paths that cause the build to fail. You should try to keep your root local directory as short as possible, for example `c:\github`, resulting in the clone being at `c:\github\odata.net`. Much longer root directories will cause build failures. 
 6. From an adminitrator command prompt, enable windows long paths by installing [tools\EnableLongPaths.reg](../tools/EnableLongPaths.reg). You can do this by simply running `EnableLongPaths.reg` as a command. Continue through any prompts
 7. From an adminitrator command prompt, open [odata.net/sln/OData.E2E.sln](OData.E2E.sln) using the previously installed Visual Studio
 8. In Visual Studio, go to `Tools -> NuGet Package Manager -> Package Manager Console`

sln/odata.md

@@ -2,7 +2,7 @@
 2. Install [.NET Core SDK 1.1.14](https://dotnet.microsoft.com/download/dotnet/1.1)
 3. Install [.NET Core SDK 2.1.818](https://dotnet.microsoft.com/download/dotnet/2.1)
 4. Despite being documented as included in .NET Core SDK 2.1.818, install [.NET Core Runtime 2.1.30](https://dotnet.microsoft.com/download/dotnet/2.1)
-5. Create a local directory for the repository, then run `git clone https://github.com/OData/odata.net.git` from the command prompt in that directory
+5. Create a local directory for the repository, then run `git clone https://github.com/OData/odata.net.git` from the command prompt in that directory. NOTE: A build issue currently exists which generates extremely long paths that cause the build to fail. You should try to keep your root local directory as short as possible, for example `c:\github`, resulting in the clone being at `c:\github\odata.net`. Much longer root directories will cause build failures. 
 6. From an adminitrator command prompt, open [odata.net/sln/odata.sln](OData.sln) using the previously installed Visual Studio
 7. In Visual Studio, go to `Tools -> NuGet Package Manager -> Package Manager Console`
 8. In the package manager console, run `Install-Package xunit.runner.visualstudio -Version 2.4.1`