## Motivation
Supplementary PR #2444 
Fix tiny bug and add loss_by_feat() to compute loss to train.
The inference process have verified to be accurate.
## Modification
- modify `sep_aspp_contrast_head.py` , add `loss_by_feat()` function to
train(training still has bug, will fix in future)
- fix testing commands path error `bash tools/dist_test.sh
projects/HieraSeg_project/` to `bash tools/dist_test.sh
projects/HieraSeg/` at README.md