Update README_ja.md (#228)

Suggested some minor translation updates to improve readability.

### What problem does this PR solve?

Suggested some minor translation updates to improve readability.

Issue link:#[Link the issue here]

### Type of change

- [ ] Bug Fix (non-breaking change which fixes an issue)
- [ ] New Feature (non-breaking change which adds functionality)
- [ ] Breaking Change (fix or feature that could cause existing
functionality not to work as expected)
- [x] Documentation Update
- [ ] Refactoring
- [ ] Performance Improvement
- [ ] Test cases
- [ ] Python SDK impacted, Need to update PyPI
- [ ] Other (please describe):