add note about the function

[marouenbg]

• added warning about sourcePPI unweighted network as a response to https://github.com/netZoo/netZooR/discussions/278

[codecov[bot]]

Codecov Report

Base: 55.74% // Head: 55.74% // No change to project coverage :thumbsup:

Coverage data is based on head (12eb365) compared to base (2a50733). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## devel #279 +/- ## ======================================= Coverage 55.74% 55.74% ======================================= Files 19 19 Lines 2411 2411 ======================================= Hits 1344 1344 Misses 1067 1067 ``` | [Impacted Files](https://codecov.io/gh/netZoo/netZooR/pull/279?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=netZoo) | Coverage Δ | | |---|---|---| | [R/sourcePPI.R](https://codecov.io/gh/netZoo/netZooR/pull/279?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=netZoo#diff-Ui9zb3VyY2VQUEkuUg==) | `100.00% <ø> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=netZoo). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=netZoo)

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