Update contribute.markdown

Drop paid membership model ad.

Author: kleinerm

contribute.markdown

@@ -17,46 +17,22 @@ highly qualified and highly focused work.
 This work is currently (year 2006 - present) mostly carried out by Mario
 Kleiner, who is now employed to do this work by the [Medical Innovations
 Incubator GmbH (MII) in Tuebingen, Germany.](https://www.mi-incubator.com)
-The MII belongs by 100% to the [non-profit foundation for medical
-innovations in Tuebingen.](http://www.mi-foundation.org)
 
 In order to fund Mario's work and provide him with the resources to do
 this job, the MII offers different types of paid services around
-Psychtoolbox and the use of Linux for neuroscience, among them a
-"Psychtoolbox Support Membership".
-
-Your lab can now financially contribute to Psychtoolbox sustainability,
-upkeep and continued improvement, by once a year buying such a
-membership for a modest fee. This membership entitles you to some
-paid support for questions regarding efficient use of Psychtoolbox,
-questions regarding the resolution of issues you may have with it, fixing
-of bugs you may encounter, and feature requests. MII also offers paid
-feature development and other commercial services.
+Psychtoolbox and the use of Linux for neuroscience, e.g., paid feature
+development and other commercial services.
 
 Please visit the following website, operated by MII, for our offering of
-commercial development services, and for the "Psychtoolbox Support Membership":
-
+commercial development services:
 
 [https://www.psychtoolbox.net](https://www.psychtoolbox.net)
 
-The membership allows you to get your voice heard by the developers
-regarding future feature development, as well as preferential treatment
-on the public Psychtoolbox user forum and GitHub issue tracker. Spare
-income generated by your membership fee, that does not have to be used
-to process paid requests made individually by you, will be used to
-fund general development and upkeep of Psychtoolbox and its ecosystem. In
-other words, it contributes to / acts as an insurance that allows
-Psychtoolbox to be around and in good shape years into the future.
-
-To clarify: Psychtoolbox itself will stay freely downloadable and useable
-by anyone, and stay fully accessible as open-source software, by anyone
-for any purpose. Anybody able and willing to contribute code and ideas of
-sufficiently high quality is invited to contribute to the open-source
-code, the documentation on this public community website and Wiki, and to
-participate and help each other on the public community forum.
-
-Professional support on the forum or the bug trackers by our main developer
-will be reserved to paying community members.
+Psychtoolbox itself will stay fully accessible as open-source software.
+Anybody able and willing to contribute code and ideas of sufficiently high
+quality is invited to contribute to the open-source code, the documentation
+on this public community website and Wiki, and to participate and help each
+other on the public community forum.
 
 Thanks for your participation and support!