Update metanorma template/stylesheet paths once https://github.com/metanorma/metanorma-cli/pull/375 is merged

Once and only once https://github.com/metanorma/metanorma-cli/pull/375 is merged **and a new metanorma-cli release is published**, run, from the top level:

```bash
find src-documents -type f -name metanorma*yml -maxdepth 1 | \
  xargs sed -i -e 's/\.\.\/\.\.\/src-documents\///'
```