[docs] Replaced straight quotations with curly quotations in instructions

Summary:
There were 3 instances where straight quotes were used instead of curly quotes in the [docs]. I took care of the first instance in https://phabricator.ashoat.com/D2358

I did not replace straight quotes which were already present (from initial commits) in config files, shell commands - the use of smart quotes there could introduce syntax errors.

Test Plan: Used vim to find the unicode instances of straight double-quotes throughout docs. After verifying they were not in code blocks, I replaced them with curly quotes.

Reviewers: atul, ashoat

Reviewed By: ashoat

Subscribers: ashoat, palys-swm, Adrian, karol-bisztyga, benschac, boristopalov

Differential Revision: https://phabricator.ashoat.com/D2422