Add basic information on the documents (#137)

* Update index.md

* Update index.md

docs/src/index.md

@@ -1,3 +1,38 @@
 # AsteroidThermoPhysicalModels.jl
 
-A package for dynamical simulation of an asteroid.
+A Julia-based toolkit for thermophysical modeling (TPM) of asteroids. It allows you to simulate the temperature distribution of the asteroid and predict non-gravitational perturbations on its dynamics. Sample notebooks are available in [Astroshaper-examples](https://github.com/Astroshaper/Astroshaper-examples).
+
+## TPM workflow
+A thermophysical simulation is performed as the following workflow.
+
+- Set ephemerides of a target asteroid(s)
+- Load a shape model(s)
+- Set thermophysical parameters
+
+After running the simulation, you will get the following output files. You should note that the thermal force and torque is calculated in the asteroid-fixed frame.
+- `physical_quantities.csv`
+    - `time`     : Time steps
+    - `E_in`     : Input energy per second on the whole surface [W]
+    - `E_out`    : Output enegey per second from the whole surface [W]
+    - `E_cons`   : Energy conservation ratio [-], ratio of total energy going out to total energy coming in during the last rotation cycle
+    - `force_x`  : x-component of the thermal force
+    - `force_y`  : y-component of the thermal force
+    - `force_z`  : z-component of the thermal force
+    - `torque_x` : x-component of the thermal torque
+    - `torque_y` : y-component of the thermal torque
+    - `torque_z` : z-component of the thermal torque
+- `subsurface_temperature.csv` : Temperature [K] as a function of depth [m] and time [s]
+- `surface_temperature.csv` : Surface temperature of every face [K] as a function of time [s]
+- `thermal_force.csv` : Thermal force on every face of the shape model [N] as a function of time
+
+## Surface/sub-surface temperature analysis
+Coming soon.
+
+## Non-Gravitational Effects
+
+### Yarkovsky effect
+Coming soon.
+
+### YORP effect
+Coming soon.
+