Update .gitignore to exclude most DLLs but include module-related DLLs

.gitignore

@@ -35,8 +35,19 @@ ScaffoldingReadMe.txt
 *.nupkg
 # NuGet Symbol Packages
 *.snupkg
-# We're including packages and PowerShell DLLs in this repository
-# to make it easier for users to get started
+# The packages folder can be ignored because of Package Restore
+**/[Pp]ackages/*
+# except build/, which is used as an MSBuild target.
+!**/[Pp]ackages/build/
+
+# NuGet tools
+nuget.exe
+
+# Exclude most DLLs
+*.dll
+
+# But include module-related DLLs
+!PowerShell/WindowsNotifications.dll
 
 # Others
 ~$*