docs: fix example config paths in English installation guide

[latent-9]

The English installation guide references example configs that 404:

• examples/v1/sft_qwen3_tiny.py (lines 71, 94)
• examples/v1/sft_intern_s1_tiny_config.py (lines 106, 270)

Both configs actually live under examples/v1/config/ — examples/v1/ contains only config/ and scripts/. Running the documented command as-is fails at Config.fromfile(...) with FileNotFoundError.

The Chinese installation guide (docs/zh_cn/get_started/installation.md) already uses the correct examples/v1/config/... paths, so this simply brings the English doc back in line.

Docs-only, no functional change.

[ErenAta16]

Verified against the tree rather than eyeballing the paths, and the change is right.

examples/v1/ on main contains only two entries, both directories:

dir  config
dir  scripts

so nothing at examples/v1/*.py resolves, and the commands in the English installation guide fail for anyone copying them. The corrected targets are both present:

examples/v1/config/  ->  19 files, including
                         sft_qwen3_tiny.py
                         sft_intern_s1_tiny_config.py

The detail that makes this straightforward to accept is that docs/zh_cn/get_started/installation.md already carries the corrected paths:

torchrun  xtuner/v1/train/cli/sft.py --model-cfg examples/v1/config/sft_qwen3_tiny.py ...
torchrun xtuner/v1/train/cli/sft.py --config examples/v1/config/sft_intern_s1_tiny_config.py

So the two translations had drifted and this brings the English one back in line rather than proposing a new convention. Worth mentioning in the description, since "which one is correct" is the first question a reviewer has on a path fix, and the Chinese doc answers it.

Both the command lines and the surrounding prose references are updated in the same diff, which is the part that usually gets half-done. Someone reading "modify the num_hidden_layers parameter in ..." needs the same corrected path as the command above it.

Looks complete for this file.