Update project-guidelines.md (dotnet/corefx#42169)

Commit migrated from https://github.com/dotnet/corefx/commit/ffb94ad2c2d7c14fd9be82d365a28a60725b4f9f

diff --git a/docs/libraries/coding-guidelines/project-guidelines.md b/docs/libraries/coding-guidelines/project-guidelines.md
index 88116aa..5466eb1 100644 (file)
--- a/docs/libraries/coding-guidelines/project-guidelines.md
+++ b/docs/libraries/coding-guidelines/project-guidelines.md
@@ -162,7 +162,7 @@ src\<Library Name>\tests - Contains the test code for a library
 ```
 
 ## ref
-Reference assemblies are required for any library that has more than one implementation or uses a facade. A reference assembly is a surface-area-only assembly that represents the public API of the library. To generate a reference assembly source file you can use the [GenAPI tool](https://www.nuget.org/packages/Microsoft.DotNet.BuildTools.GenAPI). If a library is a pure portable library with a single implementation it need not use a reference assembly at all.
+Reference assemblies are required for any library that has more than one implementation or uses a facade. A reference assembly is a surface-area-only assembly that represents the public API of the library. To generate a reference assembly source file you can use the [GenAPI tool](https://www.nuget.org/packages/Microsoft.DotNet.BuildTools.GenAPI). If a library is a pure portable library with a single implementation it need not use a reference assembly at all. Instructions on updating reference sources can be found [here](https://github.com/dotnet/corefx/blob/master/Documentation/coding-guidelines/updating-ref-source.md).
 
 In the ref directory for the library there should be at most **one** `.csproj` that contains the latest API for the reference assembly for the library. That project can contain multiple entries in its `BuildConfigurations` property.