fix docs: change some description in w2d3 documentation for tiered compaction trigger condition

[cvt220106]

1. compaction trigger precondition The original text stated that compaction triggers when the number of tiers is 'larger than' num_tiers, which could be interpreted as strictly greater than (>). This has been corrected to 'greater than or equal to (or can say reaches)' to accurately reflect the intended behavior and align with the actual implementation.
2. min_merge_width condition same as above, it should be 'at least' not 'more than'
3. reduce sorted run conditions accurately states the aim to reduce tiers to num_tiers - 1