Point to issues rather than new-issue in contribution guidelines.

Author: jatkinson1000

README.md

@@ -261,7 +261,7 @@ If you spot an issue with the materials please let us know by
 here on GitHub clearly describing the problem.
 
 If you are able to fix an issue that you spot, or an
-[existing open issue](https://github.com/Cambridge-ICCS/ml-training-material/issues/new/choose)
+[existing open issue](https://github.com/Cambridge-ICCS/ml-training-material/issues)
 please get in touch by commenting on the issue thread.
 
 Contributions from the community are welcome.

slides/index.html

@@ -293,7 +293,7 @@ <h2 id="license">License</h2>
 
           <h2 id="contribution-guidelines-and-support">Contribution Guidelines and Support</h2>
           <p>If you spot an issue with the materials please let us know by <a href="https://github.com/Cambridge-ICCS/ml-training-material/issues/new/choose" target=blank>opening an issue</a> on GitHub clearly describing the problem.</p>
-          <p>If you are able to fix an issue that you spot, or an <a href="https://github.com/Cambridge-ICCS/ml-training-material/issues/new/choose" target=blank>existing open issue</a> please get in touch by commenting on the issue thread.</p>
+          <p>If you are able to fix an issue that you spot, or an <a href="https://github.com/Cambridge-ICCS/ml-training-material/issues" target=blank>existing open issue</a> please get in touch by commenting on the issue thread.</p>
           <p>Contributions from the community are welcome. To contribute back to the repository please first <a href="https://github.com/Cambridge-ICCS/ml-training-material/fork" target=blank>fork it</a>, make the neccessary changes to fix the problem, and then open a pull request back to this repository clerly describing the changes you have made. We will then preform a review and merge once ready.</p>
           <p>If you would like support using these materials, adapting them to your needs, or delivering them please get in touch either via GitHub or via <a href="https://github.com/Cambridge-ICCS" target=blank>ICCS</a>.</p>