Add installation section

[avanobberghen]

Installation:

1. In the openMEDIS database, make sure that there is an employeeID column in the assests db table, if not then create it.
2. Copy all the above sources into a folder "api" at the root of openMEDIS
3. Update the file called config.php, and edit the URL as well as credentials. (They can be found in common.inc.php of openMEDIS)
4. In api/db folder, run the query mobile_installation_to_extend_existing.sql on the openMEIDS database. This will create fields for key in the login table.

Test it's reachable:

1. Using Chrome extension "Postman", login to the following POST at http://"domain"/api/public/v1/login, with:
   Headers: select Content type = application/json
   Body: selet "raw", and enter the contents: {"username":"","password":""} (in JSON minified)

2. open http://ideone.com/ to run the python code

import hashlib
import hmac

def calc_xhash(content, username, password):
	access = "{}{}".format(username, password).encode()
  	pk = hashlib.sha256(access).hexdigest().encode()
  	print(hmac.new(pk, content.encode(), hashlib.sha256).hexdigest())
        
calc_xhash('','<yourusername>', '<yourpassword>')

3. Test by running this GET: http://"domain"/api/public/v1/database/scheme
   Headers:
   X-PublicKey = [public key from DB login table for your username]
   X-Hash = [result of step 2]