Add install instructions to contribution guidelines

Contributing.md

@@ -11,6 +11,22 @@ Please avoid:
 - Lots of unrelated changes in one commit
 - Modifying files that are not directly related to the feature you implement
 
+## Install addin from source
+
+- Clone this repository
+  - Or, fork and clone your fork if you plan to contribute
+- Ensure your development environment meets the
+  [prerequisites](#prerequisites-for-compiling-revitlookup) from the
+  contributing guidelines
+- Run `dotnet build -c '{configuration}'`
+  - Where `{configuration}` is a string defined in [`RevitLookup.csproj`][rl-proj] at the XPath `/Project/PropertyGroup/Configurations`
+  - E.g. `dotnet build -c 'Release R23'`
+
+This will build install the project into your local Revit addins directory for
+the indicated year.
+
+[rl-proj]: source/RevitLookup/RevitLookup.csproj
+
 ## Rules
 
 - Follow the pattern of what you already see in the code
@@ -71,7 +87,7 @@ public sealed class DocumentDescriptor : Descriptor, IDescriptorResolver
             nameof(Document.PlanTopologies) => ResolvePlanTopologies,
             _ => null
         };
-        
+
         IVariants ResolvePlanTopologies()
         {
             return Variants.Single(_document.PlanTopologies);
@@ -95,14 +111,14 @@ public sealed class PlanViewRangeDescriptor : Descriptor, IDescriptorResolver
             nameof(PlanViewRange.GetLevelId) => ResolveGetLevelId,
             _ => null
         };
-        
+
         IVariants ResolveGetOffset()
         {
             return new Variants<double>(2)
                 .Add(viewRange.GetOffset(PlanViewPlane.TopClipPlane), "Top clip plane")
                 .Add(viewRange.GetOffset(PlanViewPlane.CutPlane), "Cut plane")
         }
-        
+
         IVariants ResolveGetLevelId()
         {
             return new Variants<ElementId>(2)
@@ -127,7 +143,7 @@ public sealed class UiElementDescriptor : Descriptor, IDescriptorResolver
             nameof(UIElement.GetLocalValueEnumerator) => ResolveGetLocalValueEnumerator,
             _ => null
         };
-        
+
         IVariants ResolveGetLocalValueEnumerator()
         {
             return Variants.Empty<LocalValueEnumerator>();
@@ -148,11 +164,11 @@ public sealed class DocumentDescriptor : Descriptor, IDescriptorResolver
             nameof(Document.PlanTopologies) when parameters.Length == 0 => ResolvePlanTopologies,
             _ => null
         };
-        
+
         IVariants ResolvePlanTopologies()
         {
             if (_document.IsReadOnly) return Variants.Empty<PlanTopologySet>();
-            
+
             return Variants.Single(_document.PlanTopologies);
         }
     }
@@ -277,4 +293,4 @@ For example, in the `RevitLookup/Views/Controls/DataGrid/DataGridCellTemplate.xa
 </DataTemplate>
 ```
 
-References to additional files must be registered in `RevitLookup/Views/Resources/RevitLookup.Ui.xaml`.
+References to additional files must be registered in `RevitLookup/Views/Resources/RevitLookup.Ui.xaml`.