Add CONTAINER_CACHE_SIZE documentation to README

README.md

@@ -268,6 +268,7 @@ secrets](#using-secrets) instead of environment variables.
 | Name  | Purpose | Default |
 |-------|---------|---------|
 | `CONTAINER_CACHE` | Set a path to cache downloads of the Foundry distribution archive and speed up subsequent container startups.  The path should be in `/data` or another persistent mount point in the container.  Set to `""` to disable.  ***Note***: When the cache is disabled the container may sleep instead of exiting, in certain circumstances, to prevent a download loop.  A distribution can be pre-downloaded and placed into a cache directory.  The distribution's name must be of the form: `foundryvtt-11.315.zip`| `/data/container_cache` |
+| `CONTAINER_CACHE_SIZE` | Set the maximum number of distribution versions to keep in the cache.  The minimum is `1`.  When the limit is exceeded, the oldest versions (lowest version numbers) are removed first.  Unset to disable cache size management and keep all versions.  | |
 | `CONTAINER_PATCHES` | Set a path to a directory of shell scripts to be sourced after Foundry is installed but before it is started.  The path should be in `/data` or another persistent mount point in the container. e.g.; `/data/container_patches`  Patch files are sourced in lexicographic order.  `CONTAINER_PATCHES` are processed after `CONTAINER_PATCH_URLS`.| |
 | `CONTAINER_PATCH_URLS` | Set to a space-delimited list of URLs to be sourced after Foundry is installed but before it is started.  Patch URLs are sourced in the order specified.  `CONTAINER_PATCH_URLS` are processed before `CONTAINER_PATCHES`.  ⚠️ **Only use patch URLs from trusted sources!** | |
 | `CONTAINER_PRESERVE_CONFIG` | Normally new `options.json` and `admin.txt` files are generated by the container at each startup.  Setting this to `true` prevents the container from modifying these files when they exist.  If they do not exist, they will be created as normal. | `false` |