doc: update README to include funding subsection

Signed-off-by: Renato Westphal <[email protected]>

README.md

@@ -233,6 +233,18 @@ Holo supports the following IETF RFCs and Internet drafts:
 | ietf-segment-routing-mpls@2021-05-26 | 62.50% | 0.00% | - | 23.53% | [32.76%](http://westphal.com.br/holo/ietf-segment-routing-mpls.html) |
 | ietf-segment-routing@2021-05-26 | 100.00% | - | - | - | [100.00%](http://westphal.com.br/holo/ietf-segment-routing.html) |
 
+## Funding
+
+This project is funded through [NGI Zero Core](https://nlnet.nl/core), a
+fund established by [NLnet](https://nlnet.nl) with financial support from the
+European Commission's [Next Generation Internet](https://ngi.eu) program. Learn
+more at the [NLnet project page](https://nlnet.nl/project/HoloRouting/).
+
+<div style="text-align: center;">
+  [<img src="https://nlnet.nl/logo/banner.png" alt="NLnet foundation logo" width="20%" />](https://nlnet.nl)
+  [<img src="https://nlnet.nl/image/logos/NGI0_tag.svg" alt="NGI Zero Logo" width="20%" />](https://nlnet.nl/core)
+</div>
+
 ## License
 
 This project is licensed under the [MIT license].