Update Ollama portable zip QuickStart with troubleshooting (#12846)

* Update ollama portable zip quickstart with runtime configurations

* Small fix

* Update based on comments

* Small fix

* Small fix

docs/mddocs/Quickstart/ollama_portablze_zip_quickstart.md

@@ -13,6 +13,7 @@ This guide demonstrates how to use [Ollama portable zip](https://github.com/inte
 - [Step 1: Download and Unzip](#step-1-download-and-unzip)
 - [Step 2: Start Ollama Serve](#step-2-start-ollama-serve)
 - [Step 3: Run Ollama](#step-3-run-ollama)
+- [Tips & Troubleshooting](#tips--troubleshootings)
 
 ## Prerequisites
 
@@ -36,7 +37,6 @@ Double-click `start-ollama.bat` in the extracted folder to start the Ollama serv
   <img src="https://llm-assets.readthedocs.io/en/latest/_images/ollama_portable_start_ollama.png"  width=80%/>
 </div>
 
-
 ## Step 3: Run Ollama
 
 You could then use Ollama to run LLMs on Intel GPUs as follows:
@@ -47,3 +47,36 @@ You could then use Ollama to run LLMs on Intel GPUs as follows:
 <div align="center">
   <img src="https://llm-assets.readthedocs.io/en/latest/_images/ollama_portable_run_ollama.png"  width=80%/>
 </div>
+
+## Tips & Troubleshooting
+
+### Speed up model download using alternative sources
+
+Ollama by default downloads model from [Ollama library](https://ollama.com/library). By setting the environment variable `IPEX_LLM_MODEL_SOURCE` to `modelscope`/`ollama` before [run Ollama](#step-3-run-ollama), you could switch the source from which the model is downloaded first.
+
+For example, if you would like to run `deepseek-r1:7b` but the download speed from Ollama library is quite slow, you could use [its model source](https://www.modelscope.cn/models/unsloth/DeepSeek-R1-Distill-Qwen-7B-GGUF) from [ModelScope](https://www.modelscope.cn/models) instead, through:
+
+- Open "Command Prompt" (cmd), and navigate to the extracted folder by `cd /d PATH\TO\EXTRACTED\FOLDER`
+- Run `set IPEX_LLM_MODEL_SOURCE=modelscope` in "Command Prompt"
+- Run `ollama run deepseek-r1:7b`
+
+> [!TIP]
+> Model downloaded with `set IPEX_LLM_MODEL_SOURCE=modelscope` will still show actual model id in `ollama list`, e.g.
+> ```
+> NAME                                                             ID              SIZE      MODIFIED
+> modelscope.cn/unsloth/DeepSeek-R1-Distill-Qwen-7B-GGUF:Q4_K_M    f482d5af6aec    4.7 GB    About a minute ago
+> ```
+> Except for `ollama run` and `ollama pull`, the model should be identified through its actual id, e.g. `ollama rm modelscope.cn/unsloth/DeepSeek-R1-Distill-Qwen-7B-GGUF:Q4_K_M`
+
+### Increase context length in Ollama
+
+By default, Ollama runs model with a context window of 2048 tokens. That is, the model can "remember" at most 2048 tokens of context.
+
+To increase the context length, you could set environment variable `IPEX_LLM_NUM_CTX` before [starting Ollama serve](#step-2-start-ollama-serve), as shwon below:
+
+- Open "Command Prompt" (cmd), and navigate to the extracted folder through `cd /d PATH\TO\EXTRACTED\FOLDER`
+- Set `IPEX_LLM_NUM_CTX` to the desired length in the "Command Prompt, e.g. `set IPEX_LLM_NUM_CTX=16384`
+- Start Ollama serve through `start-ollama.bat`
+
+> [!TIP]
+> `IPEX_LLM_NUM_CTX` has a higher priority than the `num_ctx` settings in a models' `Modelfile`.