Update CONTRIBUTING.md

add note on to-dos for new sumodules, they're getting overlooked almost always..

Author: megies

CONTRIBUTING.md

@@ -30,6 +30,8 @@ First, if the PR is directly related to an already existing issue (which is no P
 
 Please make sure to select the correct base branch (`master` vs. `maintenance_x.x.x`) for your PR.
 
+If your PR is adding a new submodule, please go through the [to-do items for new submodules in the wiki](https://github.com/obspy/obspy/wiki/How-to%3A-add-a-new-submodule).
+
 If you want to request an automated build of ObsPy's API docs for your PR, simply include the magic string `+DOCS` somewhere in the PR's comments. Once finished, the docs build will show up in the PR's review/commit status section alongside the results from Continuous Integration (PR docs builds can be looked up [here](http://docs.obspy.org/pull-requests/)).
 
 If any specific networking modules should be tested for the PR, e.g. when proposing changes to the FDSN client module, please include a magic string like e.g. `+TESTS:clients.fdsn` somewhere in the PR's comments. Multiple modules can be comma separated (e.g. `+TESTS:clients.fdsn,clients.iris`) or put in separate `+TESTS:...` strings, which will be accumulated across all of the PR's comments. To run *all* modules' test suites, include `+TESTS:ALL` somewhere in a comment.