Update README supported Python versions and fix issue template link

.github/ISSUE_TEMPLATE.md

@@ -1,6 +1,8 @@
 Please submit help issues to:
-https://discuss.matsci.org/c/matminer/automatminer
+https://matsci.org/c/matminer/16
 
 The Github issues is no longer used except for internal development purposes.
 
 If you are unable to use the Discourse forum, you may submit an issue here, but you must **clearly** state the reason you are unable to use the Discourse forum in your ticket. Otherwise, your issue will be **closed** without response.
+
+Please search both the forums and former GitHub issues before raising a ticket to avoid duplicating discussions.

README.md

@@ -7,7 +7,7 @@ matminer is a library for performing data mining in the field of materials scien
 - **[Help/Support Forum](https://matsci.org/c/matminer/16)**
 - **[Source Repository](https://github.com/hackingmaterials/matminer)**
 
-matminer supports Python 3.8+.
+matminer supports Python 3.9+.
 
 #### Related packages: