Add guidance on words to use with countable nouns

[julian-cable]

Guidance to add:
For countable nouns, use "fewer" instead of "less", and use "number" instead of "amount".

Original example 1:
"This passphrase configuration can improve security by providing less opportunities for someone else to see you type the passphrase."

Improvement example 1:
"This passphrase configuration can improve security by providing fewer opportunities for someone else to see you type the passphrase."

Original example 2:
"Vim has fast, efficient keystrokes to delete an exact amount of words, lines, sentences, or paragraphs."

Improvement example 2:
"Vim has fast, efficient keystrokes to delete an exact number of words, lines, sentences, or paragraphs."

[julian-cable]

Added guidance and examples.