dotnet-add-{package, reference}: add page (#11024)

* Add dotnet add *

* Update pages/common/dotnet-add-package.md

Co-authored-by: Lena <126529524+acuteenvy@users.noreply.github.com>

* Update pages/common/dotnet-add-package.md

Co-authored-by: Lena <126529524+acuteenvy@users.noreply.github.com>

* Update pages/common/dotnet-add-reference.md

Co-authored-by: Lena <126529524+acuteenvy@users.noreply.github.com>

---------

Co-authored-by: Lena <126529524+acuteenvy@users.noreply.github.com>

pages/common/dotnet-add-reference.md

@@ -0,0 +1,12 @@
+# dotnet add reference
+
+> Add .NET project-to-project references.
+> More information: <https://learn.microsoft.com/dotnet/core/tools/dotnet-add-reference>.
+
+- Add a reference to the project in the current directory:
+
+`dotnet add reference {{path/to/reference.csproj}}`
+
+- Add a reference to the specific project:
+
+`dotnet add {{path/to/project.csproj}} reference {{path/to/reference.csproj}}`