Typo correction

Replace "more clear be" with "more clear by"
Typo and phrasing change

1. Remove full stop between $X$ and :
2. Replace "computational-intensive" with "computationally-intensive"
Add acronym definition and syntax correction

1. Add (MCMC) after first mention of Markov Chain Monte Carlo
2. Correct $\\lambda$s to $\lambda$s.
Merge pull request #153 from williamscott/master

Typos and phrasing changes