Two links in generated documentation lead to 404

[gregsadetsky]

On this documentation page, under the "Relays" paragraph, there are two broken links:

• "named magic-wormhole-mailbox-server and has documentation here" (404 link)
• "Code for the Transit Relay is provided a separate package named magic-wormhole-transit-relay with instructions here" (404 link)

Both links are 404 as they - in the source .md files - link to:

• https://github.com/warner/magic-wormhole-mailbox-server/blob/master/docs/welcome.md (source link)
• https://github.com/warner/magic-wormhole-transit-relay/blob/master/docs/running.md (source link)

... but Sphinx (or read the docs?) incorrectly transforms those markdown links as it strips the .md extensions, thereby creates incorrect links.

[MiirzaBaig]

Should i resolve this Bug?

[meejah]

@I-MirzaBaig if you know how to fix it, a PR would be great!

[MiirzaBaig]

Will try my best!