Updating Submodule (#647)

* Updating Submodule

* Create SUBMODULE.md

Author: antmarakis

.gitmodules

@@ -1,3 +1,3 @@
 [submodule "aima-data"]
 	path = aima-data
-	url = https://github.com/aimacode/aima-data
+	url = https://github.com/aimacode/aima-data.git

SUBMODULE.md

@@ -0,0 +1,11 @@
+This is a guide on how to update the `aima-data` submodule. This needs to be done every time something changes in the [aima-data](https://github.com/aimacode/aima-data) repository. All the below commands should be executed from the local directory of the `aima-python` repository, using `git`.
+
+```
+git submodule deinit aima-data
+git rm aima-data
+git submodule add https://github.com/aimacode/aima-data.git aima-data
+git commit
+git push origin
+```
+
+Then you need to pull request the changes (unless you are a collaborator, in which case you can commit directly to the master).