configuration error: project.version must be pep440

README should document the need to manually replace the "SEMANTIC_VERSION" placeholder of the version attribute of the pyproject.toml file in order to achieve development installation on the main branch.

To reproduce the error:

$ pip install [-e] .
[...]
  ValueError: invalid pyproject.toml config: `project.version`.
  configuration error: `project.version` must be pep440

Currently set to c44a34e0:

$ git log -1 --oneline
c44a34e (HEAD -> main, tag: 0.0.8, gitlab/release_0.0.8, gitlab/main, gitlab/HEAD) Merge branch 'solve_env' into 'main'