Create theme_support.md

Author: ghaschel

.github/ISSUE_TEMPLATE/theme_support.md

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+---
+name: Theme support
+about: Ask for support for a specific theme, or a change in a specific theme.
+title: Support extra-matched characters colors for XYZ theme
+labels: theme support
+assignees: ghaschel
+
+---
+
+**Is your request a change or a new theme?**
+- [ ] Change
+- [ ] Request
+
+**What is the theme name and link?**
+[Community Material Theme](https://marketplace.visualstudio.com/items?itemName=Equinusocio.vsc-community-material-theme)
+
+**If it is a change, please describe what is the desired color theme**
+e.g.: Community Material Theme Darker High Contrast
+
+**Describe the suggested improvement/change**
+Please, describe the suggested improvement/change, bear in mind that, you can only work with colors that already exist in your theme.
+Theme changes will be evaluated per-request, as not all changes may be doable.
+
+**Additional context**
+Add any other context or screenshots about your request, or something you might think is relevant.