Update index.md

Transfer from README to documentation

docs/src/index.md

@@ -2,3 +2,35 @@
 
 *Bi-orthogonal bases for galactic dynamics in Julia*
 
+---
+## Installation
+
+For installation and first use test, follow the instructions on the github [README](https://github.com/JuliaStellarDynamics/AstroBasis.jl).
+
+---
+## Basis functions
+
+`AstroBasis` currently offers four different types of bases.
+### 3d
+1. Clutton-Brock (1973), which is a match to the Plummer (1911) profile.
+2. Hernquist & Ostriker (1992), which is a match to the Hernquist (1990) profile.
+
+### 2d
+1. Clutton-Brock (1972), which is a 2d match to a Plummer profile.
+2. Kalnajs (1976), which is a spiral basis.
+
+---
+
+## Common functions
+
+The common functions are detailed in `src/Basisdoc.jl`. Any instantiated basis will result in a structure, with attributes `name`, `dimension`, `lmax`, `nmax`, `rb` (the basis scale), and `G` (the gravitational constant; unity by default). The following functions are also defined:
+
+`getUln(basis,l,n,r)` will calculate the basis potential at location r for harmonic order l and radial order n.
+
+`getDln(basis,l,n,r)` will calculate the basis density at location r for harmonic order l and radial order n.
+
+Overloaded function `tabUl!(basis,l)` will fill the structure attribute `tabUl` table with radial potential values from the basis up to `nmax`.
+
+Overloaded function `tabDl!(basis,l)` will fill the structure attribute `tabUl` table with radial density values from the basis up to `nmax`.
+
+`read_and_fill_prefactors(lmax,nmax)` will load prefactors for the basis. This is called when the basis is instantiated, and is unlikely to be needed to be called externally.