Allow docs to be built without pip install of gprmax

docs/source/conf.py

@@ -6,9 +6,13 @@
 # -- Project information -----------------------------------------------------
 # https://www.sphinx-doc.org/en/master/usage/configuration.html#project-information
 
+import os
 import re
+import sys
 import time
 
+sys.path.insert(0, os.path.abspath("../.."))
+
 project = "gprMax"
 copyright = f'2015-{time.strftime("%Y")}, The University of Edinburgh, United Kingdom. Authors: Craig Warren, Antonis Giannopoulos, and John Hartley'
 author = "Craig Warren, Antonis Giannopoulos, and John Hartley"