Added initial import docs (#24)

Author: microbit-sam

README.rst

@@ -136,6 +136,29 @@ relatively small when you consider:
 * The web has caching built in (we should trust it)
 * We actually want kids to view source and find the .hex file in as raw a form as possible.
 
+Importing Projects
+++++++++++++++++++
+Python projects from external sources can be imported into the editor using a special URL e.g.
+``https://python.microbit.org/v/1.1#project:{{ encoded project }}``
+
+To encode a project, it must be structured as follows:
+
+::
+
+    {
+      meta: {
+            cloudId: "microbit.co.uk",       # optional
+            comment: "A MicroPython script", # required - may be blank
+            editor: "python",                # required - editor name
+            lastUse: 1538407830,             # optional - UNIX time the script was last used
+            name: "unearthly script 2"      # required - may be blank
+          },
+     source: "# Add your Python code here. E.g.\r\n from microbit import *\r\n while True:\r\n    display.scroll('Hello, World!')\r\nsleep(2000)"
+    }
+
+This JSON structure is compressed using `LZMA
+<https://github.com/LZMA-JS/LZMA-JS>`_, and then encoded as Base64 to include in the import URL.
+
 Configuration
 -------------