improve installation instructions
use indentation rather than fenced code blocks
Merge pull request #343 from mysociety/installation-instructions

Installation instructions
navbar improvements
whitespace fixes and css file cleanup
better spacing for user icon in navbar
rearrange css file
fix up footer styling; move poplus link to footer
remove placeholder marketing divs from homepage
profile page improvements
slightly more padding on writing interface
automatic whitespace fixes
fix up submit button spacing on letter writing page
non-functional form on empty instance page