Add GiteaMailTemplates (#186)

Add [GiteaMailTemplates](https://github.com/KenanZhu/GiteaMailTemplates) — 110 email templates across 10 visual styles for self-hosted Gitea,
  under a new `Templates` section.

  Does the new `Templates` category make sense here, or would it fit better under an existing section?

Reviewed-on: https://gitea.com/gitea/awesome-gitea/pulls/186
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-by: Nicolas <bircni@icloud.com>
Co-authored-by: KenanZhu <3471685733@qq.com>
Co-committed-by: KenanZhu <3471685733@qq.com>

README.md

@@ -34,6 +34,7 @@ Entries are grouped by maintenance status:
     - [Plugins](#plugins)
     - [Scripts](#scripts)
     - [SDK](#sdk)
+    - [Templates](#templates)
     - [Themes](#themes)
       - [Light](#light)
       - [Dark](#dark)
@@ -176,6 +177,10 @@ Entries are grouped by maintenance status:
 - [tea4j-autodeploy](https://codeberg.org/gitnex/tea4j-autodeploy) - Swagger-generated Java library which uses Retrofit to access the Gitea API `GPL-3.0` `Java`
 - [java-gitea-api](https://github.com/le-shi/java-gitea-api) - Swagger generated api for Gitea `MIT` `Java`
 
+### Templates
+
+- [GiteaMailTemplates](https://github.com/KenanZhu/GiteaMailTemplates) - A curated collection of 110 professionally designed email templates for self-hosted Gitea — 10 visual styles, drop-in ready. `MIT` `Go`
+
 ### Themes
 
 - [Catppuccin](https://github.com/catppuccin/gitea) - Soothing pastel theme for Gitea `MIT` `CSS`