Strengthen the server covenant

Explicitly reference abuse of external origin. A server that has
a code of conduct and a small number of users may never feel the
need to moderate abusive behavior. But if such a server fails
to suspend the worst routine origins of abuse in the fediverse,
it ultimately fails its users.

In practice, new users signing up, especially vulnerable folks,
may be immediately targeted by abusive actors from other servers.
Several instances of exactly this happening have been
well-documented by now.

Since this extent of moderation responsibility is non-intuitive
and non-obvious, it is important to be explicit.

pages/covenant.tsx

@@ -13,7 +13,7 @@ const Covenant = () => (
         <CovenantSection
           heading="All Mastodon servers we link to from our server picker commit to the following:"
           rules={[
-            { heading: "Active moderation against racism, sexism, homophobia and transphobia", text: "Users must have the confidence that they are joining a safe space, free from white supremacy, anti-semitism and transphobia of other platforms." },
+            { heading: "Active moderation against racism, sexism, homophobia and transphobia", text: "Users must have the confidence that they are joining a safe space, free from white supremacy, anti-semitism and transphobia of other platforms. Moderation must extend to abuse originating from other servers, e.g., by silencing or suspending servers that neglect or refuse to take action against it." },
             { heading: "Daily backups", text: "It is important for users to have the confidence that a trip over the power cable or a rogue bit flip will not erase all of their data. Having a backup strategy is a basic necessity of providing a public service." },
             { heading: "At least one other person with emergency access to the server infrastructure", text: "Various circumstances can prevent the original owner of the Mastodon server from answering technical emergencies. For this reason, more than one person must have that capability." },
             { heading: "Commitment to give users at least 3 months of advance warning in case of shutting down", text: "Sometimes services shut down, it is the cycle of life. But users must have the confidence that their account will not disappear overnight, so that they have time to export their data and find another server." }