Make the issue template even more prescriptive

Some things that seem too obvious to say apparently are not, so do say
them explicitly, as having the leftover from the template in the bug
reports is really confusing.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -7,14 +7,24 @@ assignees: ''
 
 ---
 
+IMPORTANT NOTE
+--------------
+
+This is a _template_, please **REMOVE** all the placeholders after filling in all the applicable sections as indicated, including this note.
+
+Please also note that this entry field uses [Markdown][1], which means that you need to escape any code snippets pasted here using the fenced code blocks, i.e. by putting <tt>```</tt> before and after it. Also escape, using backslash, i.e. `\<` any angle brackets to prevent them from being interpreted as HTML tags.
+
+[1]: https://docs.github.com/github/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax
+
+---
+
 **Describe the bug**
 A clear and concise description of what the bug is.
 
 **Expected vs observed behaviour**
-Please describe what you expected to happen and what actually happens.
+Please describe what you expected to happen and what actually happens. Make sure to explain what exactly is the problem, just attaching a screenshot is not always sufficient. When in doubt, please provide more details rather than too few.
 
 **Patch or snippet allowing to reproduce the problem**
-
 Please attach the smallest possible patch allowing to reproduce the problem in a sample. If there is absolutely no appropriate sample, please attach a minimal self-contained example in a single file.
 
 Skip this step if the problem can be reproduced in one of the samples without any changes.
@@ -30,7 +40,7 @@ Steps to reproduce the behaviour, please make them as detailed as possible, e.g.
  - wxWidgets version you use: [e.g. 3.1.6]
  - wxWidgets port you use: [e.g. wxMSW, wxGTK, wxOSX]
  - OS and its version: [e.g. Windows 10.0.19042.867, Ubuntu 22.10, macOS 15]
- - For wxGTK only:
+ - For wxGTK only (**remove** this if not using wxGTK)
    + GTK version: [e.g. 3.24.5]
    + Which GDK backend is used: [X11 or Wayland]
    + If relevant, i.e. for appearance-related problems: [current theme]