Walkthroughs for custom maps.

Added that SoD_SP is required. Also, the message from the first day states that the map was made for SoD_SP, and yes, some options, including obstacles, are locked. I tested it with HD+, I don't know if there will be a difference without it if the necessary plugin options are enabled.

Actually, SoD_SP is not required. Now, obstacles are always original, regardless of whether HD+ is present.