Add bug report and documentation improvement issue templates (#762)

Author: SnehaChaursia

.github/ISSUE_TEMPLATE/bug-report.yml

@@ -0,0 +1,19 @@
+name: Bug report
+description: Report a broken link, rendering issue, or incorrect content
+title: "[Bug]: "
+labels: ["bug"]
+body:
+  - type: input
+    id: url
+    attributes:
+      label: Page URL
+      placeholder: https://precice.org/some-page.html
+    validations:
+      required: true
+  - type: textarea
+    id: description
+    attributes:
+      label: What is wrong?
+      placeholder: "The link to X returns a 404. It should point to Y."
+    validations:
+      required: true

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,5 @@
+blank_issues_enabled: true
+contact_links:
+  - name: preCICE Discourse Forum
+    url: https://precice.discourse.group
+    about: For usage questions, please ask on the preCICE Discourse forum instead of opening a GitHub issue.

.github/ISSUE_TEMPLATE/documentation-improvement.yml

@@ -0,0 +1,17 @@
+name: Documentation improvement
+description: Suggest an improvement or flag missing/unclear content
+title: "[Docs]: "
+labels: ["content"]
+body:
+  - type: input
+    id: url
+    attributes:
+      label: Page URL (if applicable)
+      placeholder: https://precice.org/some-page.html
+  - type: textarea
+    id: description
+    attributes:
+      label: What should be improved?
+      placeholder: "The section on X doesn't explain Y..."
+    validations:
+      required: true