De-gadgetify the astro part of the documentation

data/astro.md

 # Astronomer 
 
-Want to get started using SWIFT? Check out the on-boarding guide available
-[here](onboarding.pdf). SWIFT can be used as a drop-in replacement for
-Gadget-2 and initial conditions in hdf5 format for Gadget can
-directly be read by SWIFT. The only difference is the parameter file
-that will need to be adapted for SWIFT. 
+Want to get started using SWIFT? Check out the on-boarding guide
+available [here](onboarding.pdf). SWIFT can be used as a replacement
+for different codes and initial conditions in hdf5 format from
+commonly used generators can directly be read by SWIFT. All you then
+need is a parameter file adapted for SWIFT!
 
 SWIFT combines multiple numerical methods that are briefly outlined
 here. The whole art is to efficiently couple them to
@@ -13,20 +13,19 @@ exploit modern computer architectures.
 ## Gravity
 
 SWIFT uses the Fast Multipole Method (FMM) to calculate gravitational
-forces between nearby particles. These forces are combined with
-long-range forces provided by a mesh that captures both the periodic
-nature of the calculation and the expansion of the simulated universe.
-SWIFT currently uses a single fixed but time-variable softening length
-for all the particles.
+forces between nearby particles. These forces can be combined with
+long-range forces provided by a mesh that captures the periodic nature
+of the calculation. SWIFT currently uses a single fixed but
+time-variable softening length for all the particles.
 
 As well as this self-gravity mode, we also make many useful external
 potentials available, such as galaxy haloes or stratified boxes that
 are used in idealised problems.
 
-Gravitational accuracy can be tuned through use of the opening angle
-and the choice of a multipole order for the short-range gravity
-calculation. The mesh forces are controlled by the cell size and
-frequency of the update.
+Besides softening, gravitational accuracy can be tuned through use of
+the adaptive opening angle and the choice of a multipole order for the
+short-range gravity calculation. The mesh forces are controlled by the
+cell size and frequency of the update.
 
 ## Cosmology
 
@@ -47,7 +46,7 @@ mode of operation of SWIFT!) when taking them from a different code.
 
 There are many hydrodynamics schemes implemented in SWIFT, and SWIFT
 is designed such that it should be simple for users to add their
-own.
+own variations.
 
 All the schemes can be combined with a time-step limiter inspired by
 the method of [Durier & Dalla Vecchia
@@ -57,6 +56,17 @@ sudden injection of energy such as in feedback events.
 
 The four main modes are as follows:
 
+### SPHENIX SPH
+
+This is our default Smoothed Particle Hydrodynamics scheme. It is
+fully described by [Borrow
+2022](http://adsabs.harvard.edu/abs/2022MNRAS.511.2367B). The core
+equations use a density-energy formulation of the equations of motion.
+This is combined with a variable artificial viscosity and
+conduction. These are accompanied by limiters to only apply these
+extra terms where they are necessary. This scheme was designed with
+galaxy formation applications in mind.
+
 ### Minimal SPH
 
 In this mode SWIFT uses the simplest energy-conserving SPH scheme that
@@ -77,7 +87,10 @@ viscosity scheme with a
 [Balsara](https://www.ideals.illinois.edu/handle/2142/23836)
 switch. Note that the GADGET-2 SPH scheme is implemented to be the
 same as in the public release of GADGET-2. This is to enable users to
-use SWIFT as a drop-in replacement for GADGET-2.
+use SWIFT as a drop-in replacement for GADGET-2 and of course for
+comparison exercises!
+
+<!--
 
 ### Pressure-Entropy SPH
 
@@ -109,6 +122,8 @@ diffusion but also comes at a higher computational cost.
 <div class="videowrapper"><iframe width="100%" height="100%" src="https://www.youtube.com/embed/sce-AWTbXFI" frameborder="0" allowfullscreen></iframe>
 </div>
 
+-->
+
 ## Subgrid models for galaxy formation
 
 SWIFT implements two main models to study galaxy formation. These are
@@ -160,8 +175,7 @@ the classic method of post-processing simulations after they are run.
 ## Documentation and tests
 
 There is a large amount of background reading material available in the
-theory directory provided with SWIFT. You will need pdflatex to build
-this documentation.
+theory directory provided with SWIFT. 
 
 SWIFT also provides a large library of hydrodynamical test cases for you to
 use, the results of which are available on our developer Wiki