zsh README improvements

[bkane-msft]

• fling example
• syntax highlighting for code blocks
• spellcheck
• replace exa? (deprecated)
• diff linux paths
• fork fasd
• homebrew centos install instructions

[bkane-msft]

Also add meld diff tool to favorite apps

[bkane-msft]

Add brew install git-delta to git notes

If you don't, you get errors like:

$ git log
  -interval int
    	Reporting and binning interval in seconds (default 5)
  -limit int
    	Limit the max number of entries for each category. 0 for no limit. (default 5)
  -logfile string
    	Log file from which we will be measuring traffic
  -tier string
    	Provide the tier's appname instead of the full path. Overrides logfile argument.