Add basic installation instructions for Fedora.

[voxik]

These are just really basic instructions discussed in sparklemotion/nokogiri#1983. Of course there could probably be recommendations to use gem install nokogiri -- --use-system-libraries as well as gem install nokogiri, but that would be just more confusing IMO.

[flavorjones]

@voxik Thank you for this work! Will merge and publish now.

[ai]

@voxik @flavorjones how we can use the system installed Nokogiri with bundler?

I still get an error:

bundle install

…
Fetching nokogiri 1.10.9 (was 1.10.7)
Installing nokogiri 1.10.9 (was 1.10.7) with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

current directory:
/home/ai/Dev/autoprefixer-rails/.bundle/ruby/2.7.0/gems/nokogiri-1.10.9/ext/nokogiri
/usr/bin/ruby -I /usr/share/rubygems -r
./siteconf20200323-204764-hjg6v0.rb extconf.rb
/usr/share/rubygems/rubygems/core_ext/kernel_require.rb:92:in
`require': cannot load such file -- did_you_mean (LoadError)
from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:92:in
`require'
        from <internal:gem_prelude>:2:in `<internal:gem_prelude>'

extconf failed, exit code 1

Gem files will remain installed in
/home/ai/Dev/autoprefixer-rails/.bundle/ruby/2.7.0/gems/nokogiri-1.10.9
for inspection.
Results logged to
/home/ai/Dev/autoprefixer-rails/.bundle/ruby/2.7.0/extensions/x86_64-linux/2.7.0/nokogiri-1.10.9/gem_make.out

An error occurred while installing nokogiri (1.10.9), and
Bundler cannot continue.
Make sure that `gem install nokogiri -v '1.10.9' --source
'https://rubygems.org/'` succeeds before bundling.

In Gemfile:
  rails was resolved to 6.0.2.2, which depends on
    actioncable was resolved to 6.0.2.2, which depends on
      actionpack was resolved to 6.0.2.2, which depends on
        actionview was resolved to 6.0.2.2, which depends on
          rails-dom-testing was resolved to 2.0.3, which depends on
            nokogiri

[flavorjones]

@ai Please open an issue under https://github.com/sparklemotion/nokogiri

[ai]

@flavorjones done sparklemotion/nokogiri#2014