[Example] Add memory control example (#152)

Author: jiarong0907

examples/02_memory_control/README.md

@@ -0,0 +1,50 @@
+# Memory monitoring and control via kvcached CLI
+
+kvcached includes a built-in CLI tool that allows you to monitor GPU memory usage and manage memory limits across different applications. A command `kvctl` is installed along with kvcached package:
+
+```bash
+kvctl
+
+# if kvcached is installed in source
+cd <kvcached-source-dir>/kvcached/cli
+python kvctl.py
+```
+
+Once inside the CLI, type `help` to view all supported commands:
+
+```
+kvcached> help
+Available commands:
+  list [ipc ...]               List IPC segments and usage
+  limit <ipc> <size>           Set absolute limit (e.g. 512M, 2G)
+  limit-percent <ipc> <pct>    Set limit as percentage of total GPU RAM
+  watch [-n sec] [ipc ...]     Continuously display usage table
+  kvtop [ipc ...] [--refresh r]  Launch curses kvtop UI (q to quit)
+  !<shell cmd>                 Run command in system shell
+  help                         Show this help message
+  delete <ipc>                 Delete IPC segment and its limit entry
+  exit | quit                  Exit the shell
+
+kvcached>
+```
+
+Use the `kvtop` command for real-time visualization of memory usage:
+
+<!-- KVCache memory monitor (muted colours) -->
+<pre>
+<span style="color:#009ACD; font-weight:bold;">KVCache Memory Usage</span>
+
+<span style="color:#009ACD;">IPC: SGLANG</span>
+<span style="color:#009ACD;">[</span><span style="color:#B7A800;">==</span><span style="color:#009E8F;">##################</span><span style="color:#666666;">----------------------------------------</span><span style="color:#009ACD;">]</span>
+Prealloc: 792.0&nbsp;MB | Used: 11.2&nbsp;GB / 39.9&nbsp;GB (30.1%) | Free: 27.9&nbsp;GB
+
+<span style="color:#009ACD;">IPC: VLLM</span>
+<span style="color:#009ACD;">[</span><span style="color:#B7A800;">==</span><span style="color:#009E8F;">#######</span><span style="color:#666666;">--------------------------------------------------- </span><span style="color:#009ACD;">]</span>
+Prealloc: 768.0&nbsp;MB | Used: 3.6&nbsp;GB / 37.4&nbsp;GB (11.7%) | Free: 33.0&nbsp;GB
+
+<span style="color:#009ACD;">GPU Memory Usage</span>
+<span style="color:#009ACD;">[</span><span style="color:#B7A800;">########################################</span><span style="color:#666666;">--------------------</span><span style="color:#009ACD;">]</span>
+Used: 52.9&nbsp;GB / 79.2&nbsp;GB (66.8%) | Free: 26.3&nbsp;GB
+
+<span style="color:#555555;">Press 'q' to quit</span>
+</pre>