Add forum links (#5282)

.github/ISSUE_TEMPLATE/config.yml

@@ -10,6 +10,6 @@ contact_links:
   - name: Show and tell
     about: Show what you built with LangChain
     url: https://github.com/langchain-ai/langgraph/discussions/categories/show-and-tell
-  - name: Slack
-    url:  https://www.langchain.com/join-community
-    about: General community discussions
+  - name: LangChain Forum
+    url:  https://forum.langchain.com/
+    about: General community discussions and support

docs/mkdocs.yml

@@ -289,6 +289,7 @@ nav:
     - Case studies: adopters.md
     - concepts/faq.md
     - llms.txt: llms-txt-overview.md
+    - LangChain Forum: https://forum.langchain.com/
     - Troubleshooting:
         - Errors:
           - troubleshooting/errors/index.md