Wrap pip error with MLEM error

[aguschin]

$ mlem build venv --model lyrics2emoji --current_env True
⏳️ Loading model from lyrics2emoji.mlem
💼 Detected the virtual env /Users/aguschin/Git/iterative/mlem/emoji/.venv
💼 Installing the required packages...
ERROR: You must give at least one requirement to install (see "pip help install")
❌ Error running pip
Command '['/Users/aguschin/Git/iterative/mlem/emoji/.venv/bin/python', '-m', 'pip', 'install']' returned non-zero exit status 1.

[aguschin]

Plus another mistake here:

(.venv) $ mlem build venv --model lyrics2emoji --current_env True
⏳️ Loading model from lyrics2emoji.mlem
💼 Detected the virtual env /Users/aguschin/Git/iterative/mlem/emoji/.venv
💼 Installing the required packages...
...
Successfully installed numpy-1.23.5 scikit-learn-1.1.1 torch-1.13.0
✅  virtual environment `venv` is ready, activate with `source venv/bin/activate`

Should be

✅  virtual environment `.venv` is ready, activate with `source .venv/bin/activate`