Update broken links, add new sponsor

Contributing-to-Mastodon/Sponsors.md

@@ -29,3 +29,4 @@ These people make the development of Mastodon possible through [Patreon](https:/
 - [Jessica Hayley](https://mastodon.social/users/jayhay)
 - [Niels Roesen Abildgaard](http://hypesystem.dk/)
 - [Zatnosk](https://github.com/Zatnosk)
+- [Spex Bluefox](https://mastodon.social/users/Spex)

README.md

@@ -17,6 +17,7 @@ Index
 ### Running Mastodon
 - [Production guide](Running-Mastodon/Production-guide.md)
 - [Development guide](Running-Mastodon/Development-guide.md)
+- [Administration guide](Running-Mastodon/Administration-guide.md)
 
 ### Contributing to Mastodon
 - [Sponsors](Contributing-to-Mastodon/Sponsors.md)