No you aren't missing anything. We do not have a guide about leveling a priest. I did write a Beginner Priest Guide on H2P. It isn't focused just on leveling a shadow priest but there might be some useful information for you there.
If you have any specific questions though some people here might be able to help you.
Are you only wanting a guide that's on MMO-Champion? Or do you mean you can't find one anywhere.
If you mean on MMO-Champion, there may not be one. As much as the site has evolved to cover the whole game, a lot of the guides are still centered around endgame/new content, and as such are more gearing/mechanics changes that reflect the most current patch or expansion.
If you mean everywhere, well, I don't know what to tell you because they're out there. You might have to look somewhat hard for one that's nice and updated, but it shouldn't be that difficult to find (or to just use a slightly out of date one, and compare against other sources).
+1 for WoW Pro. Great addon for smashing through quests and levels. Guildies criticize it for "making you dumb" but when im on my 4th alt and only have ~1-2 hours of free time available, youd better believe im optomizing my time
And not to give the elitist response, but really no guide should be necessary before 60. 1-60 *is* the guide by how hand-holding easy it is to get through it. You have a basic (albeit bland) array of starting abilities and you have plenty of time to explore how each one works and whats better to use and when. Then as the levels come in they introduce new abilities for you to try and fit into the puzzle. If you're still struggling at 60, then a guide might be necessary.
Same answer for talents. Even if you choose "wrong" (its pretty hard to), it wouldnt really matter till around 60 or so. You can honestly just pick what sounds like it would be helpful.
Edit: (Why do I have an afterthought on every post?!) I will say that one thing that probably isnt apparent is getting the (Major)Glyph of Spirit Tap. This definitely helps with downtime and paired with the talent Masochism, always ends up returning mana one way or another. (Prime)Glyph of SWD lets you "double tap" for mana, but probably not a good first choice. (SW: Death trained at 32, glyphs available at 35, Masochism as early as 41)