REDME.md update

Author: zhubonan

README.md

@@ -28,16 +28,32 @@ Try interactively
 Interactive jupyter notebook examples can be found in the `examples` folder.
 Click the *binder* badge above to launch these examples in a pre-built environment and try it in your browser!
 
-Requirements
+Dependences
 -----------
 * [ase](https://wiki.fysik.dtu.dk/ase/): The atomic simulation environment
 * [castepinput](https://gitlab.com/bz1/castepinput): A light weight writer/reader for the input files of [CASTEP](www.caste.org).
 
+Installation
+-----------
+
+The package can be installed from pypi together with the dependencies:
+
+```
+pip install airsspy
+```
+
+Alternative, one can also install directly from the repository (defaults to the master branch):
+
+```
+pip install git+https://github.com/zhubonan/airsspy
+```
+
 Usage
 -----
 Assuming you are familiar with `ase`, python and has some basic knowledge of AIRSS.
 To prepare a seed for generating a *sensible* random structure:
-```
+
+```python
 from airsspy import SeedAtoms
 seed = SeedAtoms('C6')
 seed.buiid.varvol = 20
@@ -51,7 +67,8 @@ for i in range(0, 6, 2):
 ```
 
 To write the seed file onto the disk:
-```
+
+```python
 atoms.write_seed('C6.cell')
 # With IPython
 # Use the buildcell executable to generate the file
@@ -61,14 +78,15 @@ atoms.write_seed('C6.cell')
 To generate a cell we can create a `Buildcell` instance,
 which is helping wrapper to the `buildcell` program of AIRSS:
 
-```
+```python
 from airsspy import Buildcell
 buidcell = Buildcell(seed)
 random_atoms = builcell.generate()
 ```
 
 A shortcut is also available as an method of the `SeedAtoms`:
-```
+
+```python
 random_atoms = seed.build_random_atoms()
 ```