Update README for colab/download options.

Author: cwant

README.md

@@ -18,7 +18,20 @@ Or in a Jupyter notebook:
 
 ### Getting the notebooks
 
-To get the notebooks that make up this course, either use git to clone the repository at Github:
+To get the notebooks that make up this course, you can either use them in
+Google Colab, or download them to your own computer.
+
+#### Opening notebooks on Colab:
+
+* Go to File->Open notebook
+* Select "Github" tab
+  * Organization: ualberta-rcg (important: press enter)
+  * Repository: ualberta-rcg/python-plotting
+  * Choose the notebook you want
+
+#### Getting notebooks on your computer:
+
+Either use git to clone the repository at Github:
 
 ```
 git clone https://github.com/ualberta-rcg/python-plotting.git
@@ -29,7 +42,16 @@ git clone https://github.com/ualberta-rcg/python-plotting.git
 ... or run the following in a Jupyter notebook:
 
 ```
-!wget -O python-plotting-master.zip https://github.com/ualberta-rcg/python-plotting/archive/master.zip
-!unzip python-plotting-master.zip
-```
+# Downloads and extracts to python-plotting-master directory
+# Warning (overwrites notebooks if they exist)
+import os, urllib.request, zipfile
+def get_notebooks():
+  url = 'https://github.com/ualberta-rcg/python-plotting/archive/master.zip'
+  zip_file = 'python-plotting.zip'
+  if os.path.exists(zip_file): return
+  urllib.request.urlretrieve(url, zip_file)
+  with zipfile.ZipFile(zip_file) as zip_ref:
+    zip_ref.extractall()
 
+get_notebooks()
+```