docs: add new markdown file for alternative markdown editors

Added a new markdown file under the `alternatives` directory to document alternative markdown editors and their features. The file includes a comparison table of different editors based on various criteria such as citation, cloud integration, image support, migration method, open-source status, plain text storage, search functionality, slides support, tags filtering, and typography enhancements.

docs/.gitignore

@@ -1,2 +1,5 @@
-!index.md
-*.md
+acg.md
+alternatives.md
+github.md
+languages.md
+websites.md

docs/alternatives/markdown.md

@@ -0,0 +1,23 @@
+# Markdown
+
+1. **Citation**: Integration with BibTeX / CSL JSON / [Zotero](https://www.zotero.org)
+2. **Cloud**: Free sync service / method
+3. **Image**: Supports pasting pictures directly
+4. **Math**: [MathJax](https://www.mathjax.org) / [KaTeX](https://katex.org) + [Mermaid](https://mermaid.js.org)
+5. **Migration**: Complete migration method
+6. **OSS**: Open Source Software
+7. **Plain Text**: Store documents in plain text
+8. **Search**: Workspace-wide search
+9. **Slides**: [reveal.js](https://revealjs.com)
+10. **Tags**: Filter documents by multiple tags
+11. **Typography**: Language-neutral replacement + quotes beautification
+
+| Name                                |      Citation      |       Cloud        |       Image        |     Migration      |        OSS         |     Plain Text     |       Search       |       Slides       |        Tags        |     Typography     |
+| ----------------------------------- | :----------------: | :----------------: | :----------------: | :----------------: | :----------------: | :----------------: | :----------------: | :----------------: | :----------------: | :----------------: |
+| [AFFiNE](https://affine.pro)        |        :x:         | :white_check_mark: | :white_check_mark: |        :x:         | :white_check_mark: |        :x:         | :white_check_mark: |        :x:         | :white_check_mark: |        :x:         |
+| [Logseq](https://logseq.com)        | :white_check_mark: |        :o:         | :white_check_mark: | :white_check_mark: | :white_check_mark: | :white_check_mark: | :white_check_mark: | :white_check_mark: |        :o:         |                    |
+| [MarkText](https://www.marktext.cc) |        :x:         |        :o:         | :white_check_mark: | :white_check_mark: | :white_check_mark: | :white_check_mark: | :white_check_mark: |        :x:         |        :x:         |        :x:         |
+| [Notion](https://www.notion.so)     |                    | :white_check_mark: |                    |                    |        :x:         |                    |                    |                    |                    |                    |
+| [Typora](https://typora.io)         |        :x:         |        :o:         | :white_check_mark: | :white_check_mark: |        :x:         | :white_check_mark: | :white_check_mark: |        :x:         |        :x:         | :white_check_mark: |
+| [VNote](https://app.vnote.fun)      |        :x:         |        :o:         | :white_check_mark: | :white_check_mark: | :white_check_mark: | :white_check_mark: | :white_check_mark: |        :x:         |        :o:         | :white_check_mark: |
+| [Zettlr](https://zettlr.com)        | :white_check_mark: |        :o:         |        :o:         | :white_check_mark: | :white_check_mark: | :white_check_mark: | :white_check_mark: |        :x:         |        :o:         |        :x:         |