revise "country that censors Tor" text

The alpha Tor Launcher UI includes the following text on the first setup screen: Click “Configure” to adjust network settings if you are in a country that censors Tor (such as China, Iran, Syria) or if you are connecting from a private network that requires a proxy.

We should change this text based on data from OONI, which as of early December 2017 indicates that the primary countries where vanilla Tor is blocked are Egypt, China, and Turkey.

Related ticket: legacy/trac#24527 (moved).