Update documentation to correct a typo (#2887)

* (doc) Fixed spelling mistake

futhur -> further

* (maint) Add doc output folder to .gitignore

Author: gep13

.gitignore

@@ -127,3 +127,4 @@ config.wyam.hash
 config.wyam.packages.xml
 /tests/integration/core/build
 /tests/integration/full/build
+docs/output

docs/input/docs/usage/msbuild.md

@@ -53,7 +53,7 @@ versioning your assemblies.
 
 ### WPF specific concerns
 
-One futhur step needs to be taken for SDK-style WPF projects.
+One further step needs to be taken for SDK-style WPF projects.
 
 Building projects with .NET Core SDK with a version lower than v5.0.200
 requires turning off automatic generation of the different versioning attributes.