Add project planning docs and repo scaffolding

Vision, requirements, tech stack, and phased roadmap for the space
survival game, plus Unreal-appropriate .gitignore/.gitattributes
and Git LFS setup.

.gitignore

@@ -0,0 +1,29 @@
+# Unreal Engine
+Binaries/
+Build/
+DerivedDataCache/
+Intermediate/
+Saved/
+.vs/
+*.VC.db
+*.opensdf
+*.opendb
+*.sdf
+*.sln
+*.suo
+*.xcodeproj
+*.xcworkspace
+
+# Generated project files (regenerated via "Generate Visual Studio project files")
+*.vcxproj
+*.vcxproj.filters
+*.vcxproj.user
+*.vcxproj.opendb
+
+# Compiled/packaged builds
+Plugins/*/Binaries/
+Plugins/*/Intermediate/
+
+# OS
+.DS_Store
+Thumbs.db