Add clarifications to the installation report documentation
The `--report` option of the pip install command produces a detailed JSON report of what
it did install (or what it would have installed, if used with the `--dry-run` option).
+```{note}
+When considering use cases, please bear in mind that
+
+- while the `--report` option may be used to implement requirement locking tools (among
+ other use cases), this format is *not* meant to be a lock file format as such;
+- there is no plan for pip to accept an installation report as input for the `install`,
+ `download` or `wheel` commands;
+- the `--report` option and this format is intended to become a supported pip feature
+ (when the format is stabilized to version 1);
+- it is however *not* a PyPA interoperability standard and as such its evolution will be
+ governed by the pip processes and not the PyPA standardization processes.
+```
+
## Specification
The report is a JSON object with the following properties:
