minor fix of formatting & typo (#1522)

* fix typsetting by adding escapes to $

* add missing "log"

to be consistent with previous definition of alpha

* !fixup 06edb64

docs/src/for-developers/interface.md

@@ -161,7 +161,7 @@ As a refresher, Metropolis-Hastings implements a very basic algorithm:
 Of course, it's much easier to do this in the log space, so the acceptance probability is
 more commonly written as 
 
-$$\alpha = \min\Big[\log \pi(θ'\_t) - \log \pi(θ\_{t-1}) + \log q(θ\_{t-1} \mid θ'\_t) - \log q(θ'\_t \mid θ\_{t-1}), 0\Big]$$
+\$\$\log \alpha = \min\Big[0, \log \pi(θ'\_t) - \log \pi(θ\_{t-1}) + \log q(θ\_{t-1} \mid θ'\_t) - \log q(θ'\_t \mid θ\_{t-1}) \Big]\$\$
 
 In interface terms, we should do the following: