Convert the crash issue template to a form

.github/ISSUE_TEMPLATE/01_crash.yml

@@ -0,0 +1,68 @@
+name: "Crash report"
+description: "rinohtype fails to produce a valid PDF file"
+labels: ["bug", "crash"]
+body:
+  - type: markdown
+    attributes:
+      value: >
+        Thanks for taking the time to fill out this bug report! ❤️
+        
+        
+        Sometimes bugs have already been fixed in the master branch. Please try to
+        reproduce the crash with the current master version of rinohtype before you
+        file a bug report. You can install it directly from GitHub:
+
+            pip install https://github.com/brechtm/rinohtype/archive/refs/heads/master.zip
+
+        Please provide the following information to make your bug report as useful as
+        possible.
+  - type: checkboxes
+    attributes:
+      label: Is there an existing issue for this?
+      description: Please search the issues to see if an issue already exists
+                   for the bug you encountered.
+      options:
+      - label: I have searched the existing issues
+        required: true
+  - type: textarea
+    id: messages
+    attributes:
+      label: Sphinx or rinoh output
+      description: The messages output by rinohtype (and Sphinx) when rendering
+                   the document.
+      render: text
+    validations:
+      required: true
+  - type: textarea
+    id: source
+    attributes:
+      label: Source files
+      description: The Sphinx project files or inputs to rinoh that cause the crash.
+                   Please note that these are crucial for reproducing the crash! You
+                   can provide any additional information that may be useful here.
+      placeholder: |
+        - insert a link to the input files (e.g. a Sphinx project repository), or
+        - attach an archive (e.g. zip) containing the source files
+
+        If you cannot share the source files publicly, try to create dummy input
+        files that reproduce the bug (may be difficult). Alternatively, you can send
+        the input files to me privately at [email protected] (I will not share them
+        with others, of course).
+    validations:
+      required: true
+  - type: textarea
+    id: versions
+    attributes:
+      label: Versions
+      description: Version information for rinohtype, Sphinx, Python and your operating system
+      placeholder: |
+        Paste the output of `rinoh --versions` (trailing _s_!), for rinohtype >= 0.5.4
+
+        Otherwise, the output of:
+          rinoh --version
+          sphinx-build --version
+          python --version
+          python -c "import platform; print(platform.platform())"
+      render: text
+    validations:
+      required: true