CONTRIBUTING: Add clause against capitalism

Thanks again GoToSocial's stub CoC.
https://codeberg.org/superseriousbusiness/gotosocial/src/commit/9b7db51436/CODE_OF_CONDUCT.md

skip-changelog.

Signed-off-by: Maxime “pep” Buquet <[email protected]>

Author: Ppjet6

CONTRIBUTING.md

@@ -24,6 +24,9 @@ tooling. "AI" models are trained at the expense of underpaid workers filtering
 inputs of abhorrent content, and does not respect the owners of input content.
 Ethically, it sucks.
 
+Nor will we accept changes (code or otherwise) that move xmpp-rs crates toward
+enterprise / surveillance / other toxic capitalist pursuits.
+
 ## Keep commits short and meaningful
 
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