docs on multi (#78)

Author: TomasVotruba

README.md

@@ -296,6 +296,44 @@ vendor/bin/swiss-knife spot-lazy-traits src --max-used 4
 That's it! Run this command once upon a time or run it in CI to eliminate traits with low value to exists. Your code will be more robuts and easier to work with.
 
 
+<br>
+
+## 12. Mutual Private Repository Dependencies
+
+Do you have a project that uses 5 private repositories? And another one that uses different 3 private repositories? Are their open-source dependencies up to date?
+
+In such situations, we want to get a quick idea about the weakest link. Do all those repositories use the same version of "symfony/console"? What about their min PHP versions?
+
+<br>
+
+That's where `multi-package-composer-stats` comes. Feed it the links to dependency repositories you want to know versions for:
+
+```bash
+vendor/bin/swiss-knife multi-package-composer-stats private-company/private-repository.git \
+    private-company/another-private-repository.git
+```
+
+↓
+
+<kbd>
+    <img src="https://pbs.twimg.com/media/GhfcUmoXkAAFA1S?format=png" style="max-width:15em">
+</kbd>
+
+<br>
+<br>
+<br>
+
+Do you want to compare **the main projects** and themselves and fetch their dependencies automatically? Provide urls to the repositories and the `--is-source` option:
+
+```bash
+vendor/bin/swiss-knife multi-package-composer-stats private-company/first-project.git \
+    private-company/another-project.git
+```
+
+Now all the dependencies are fetched per provided project from the `"repositories"` section of `composer.json`.
+
+That's it!
+
 <br>
 
 Happy coding!