Removed some tags that were causing compilation issues

Moved old RTD around.

Added rtd-specific gitignore

Added 'new' RTD system

Added tempaltes of how to add new items to the documentation

Added HydroSchemes information

Added information from the onboarding guide into the online documentation, as well as adding the makefile

Add Equation of State documentation

Added the onboarding guide stuff

Added initial conditions section

Add eos documentation

Removed git marks

added minor change to the particle type table to make it fully consistent with SWIFT

Implemented Matthieu's changes

Updated information about minimalsph

removed statement about balsara switch

Add Cooling doc

Add cooling and update structure

Minor tidy up

Renamed section