Update README.md

README.md

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 This is a little docker image for histing static content efficiently.
 **Supports ETags & Brotli/GZip** compression out of the box.
 
+Automatically builds the latest mainline and stable releases weekly.
+
+## Tags
+
+Tags follow the official nginx naming convention.
+
+- `mainline`, same as `latest`
+- `stable`
+- Specific version
+
 ## Quickstart 🚀
 
 ```yaml