Add info from #1273

Author: Dhghomon

src/content/doc-surrealdb/cli/env.mdx

@@ -560,6 +560,11 @@ These environment variables are used to configure the storage backend for Surrea
       <td scope="row" data-label="Default">4096</td>
       <td scope="row" data-label="Notes"></td>
     </tr>
+    <tr>
+      <td scope="row" data-label="Env var"><code>SURREAL_ROCKSDB_BLOCK_CACHE_SIZE</code></td>
+      <td scope="row" data-label="Default">Whichever is larger of "System total memory / 2 - 1GiB" and "512MiB"</td>
+      <td scope="row" data-label="Notes">RocksDB <a href="https://github.com/facebook/rocksdb/wiki/memory-usage-in-rocksdb">block cache size</a> in bytes</td>
+    </tr>
     <tr>
       <td scope="row" data-label="Env var"><code>SURREAL_ROCKSDB_KEEP_LOG_FILE_NUM</code></td>
       <td scope="row" data-label="Default">20</td>