Begin sandboxing support, README updates.

cache/fscache.cpp

@@ -7,7 +7,7 @@ FsCache::FsCache(std::string path)
 {
 	if(!std::filesystem::exists(path))
 	{
-		throw std::runtime_error { "Directory does not exist" };
+		throw std::runtime_error { "Cache directory does not exist" };
 	}
 	this->path = path;
 }