Include sponsorship section (#2063)

* Include sponsorship section

* Create FUNDING.yml

* Describe how funds are used

Co-authored-by: Pepe Iborra <pepeiborra@gmail.com>

Co-authored-by: Pepe Iborra <pepeiborra@gmail.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Author: 3 people

FUNDING.yml

@@ -0,0 +1 @@
+open_collective: haskell-language-server

README.md

@@ -875,3 +875,7 @@ This will typically provide instructions for how to support new languages.
 
 In some cases you may need to write a small bit of additional client support, or expose a way for the user to set the server's [configuration options](#configuring-haskell-language-server) and
 for them to configure how the server is started.
+
+### Sponsorship
+
+If you want to contribute financially you can do so via [open-collective](https://opencollective.com/haskell-language-server). In the past the funding has been used to sponsor [summer student projects](https://mpickering.github.io/ide/posts/2021-07-22-summer-of-hls.html).