Add Liberapay link to README.md (#6563)

Signed-off-by: Marcin Mikołajczak <me@m4sk.in>

README.md

@@ -17,9 +17,10 @@ Click on the screenshot below to watch a demo of the UI:
 
 **Ruby on Rails** is used for the back-end, while **React.js** and Redux are used for the dynamic front-end. A static front-end for public resources (profiles and statuses) is also provided.
 
-If you would like, you can [support the development of this project on Patreon][patreon]. Alternatively, you can donate to this BTC address: `17j2g7vpgHhLuXhN4bueZFCvdxxieyRVWd`
+If you would like, you can [support the development of this project on Patreon][patreon] or [Liberapay][liberapay]. Alternatively, you can donate to this BTC address: `17j2g7vpgHhLuXhN4bueZFCvdxxieyRVWd`
 
 [patreon]: https://www.patreon.com/user?u=619786
+[liberapay]: https://liberapay.com/Mastodon/
 
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