update performance translation.
Add mention to Network Conditioning feature

Google Chrome has added a feature to its DevTools that throttles
the speed of a connection, emulating limited network conditions.

Fixes #964.
fix some sentences
More RTL support to fix navigation menus and footers
Fix bits per image channel calculation.
Fix landing pages to fall back to en
Restrict fallback to en
Have sub articles appear on landing
Fixes some odd quotes and other l10n artifacts.
Fixes meta-color and changes dist-&-disc to blue
Updates to betterbook to add distribution and discovery
Minor clean up for dist & discovery
Fixes #883
Adding landing pages to translatable pages
Merge pull request #972 from JamieMason/master

Image optimization: Fix bits per image channel calculation.
Merge pull request #970 from chenxsan/fix-chinese

Updated translations
Merge pull request #969 from jacquerie/issue-964

Add mention to Network Conditioning feature
Merge pull request #963 from appleboy/patch-1

update performance translation.
Fixes multi-lang issue