Update list of make checks

.github/CONTRIBUTING.md

@@ -9,5 +9,5 @@ Please join us on [chat](https://chat.awesome-selfhosted.com) to clarify any que
  * Non-[Free](https://en.wikipedia.org/wiki/Free_software) software must be marked `⊘ Proprietary` next to the title, and added to [non-free.md](non-free.md).
  * The `⚠` character must be inserted for software that relies on a third party service the user does not control, e.g ``[Name](http://homepage/) `⚠` - Short description...``.
  * Check current [issues](https://github.com/Kickball/awesome-selfhosted/issues) and [Pull Requests](https://github.com/Kickball/awesome-selfhosted/pulls), as well as [closed issues/PRs](https://github.com/Kickball/awesome-selfhosted/pulls?utf8=%E2%9C%93&q=is%3Aclosed+).
- * The list of contributors can be updated with `make contrib`. Several checks are available: `make noexternallink; make missinglicenselanguage; make nofullstop` 
+ * The list of contributors can be updated with `make contrib`. Several checks are available: `make noexternallink; make nolicenselanguage; make nofullstop; make longdescriptions; make listlicenses; make syntaxerrors` or run all with `make checks`.
  * Software with no development activity for 6-12 months may be removed from the list.