Add endorsement by Foundation for Public Code

[Ainali]

Changes proposed in this pull request:

• Adding endorsement by Foundation for Public Code.

Propagation of Changes

Identify where of the following the proposed changes need to be propagated, and include the relevant pull request where appropriate:

• [ ] The DPGA website contains https://digitalpublicgoods.net/standard/ which needs to be updated manually matching the contents of standard.md.
• [ ] The DPGA website also contains the submission guide which needs to be updated manually.
• [ ] The DPG application webapp admin panel which will be updated manually.
• [ ] The Eligibility Form through the unicef/publicgoods-scripts repository, by editing quizQuestions.js

[ricardomiron]

We have now deprecated endorsements in favor of membership.