allow input from stdin via pipe instead of editor

[8go]

Is your feature request related to a problem? Please describe.
No problem. Just an idea for a new feature.

Describe the solution you'd like
Currently stdin input is not supported:
$ echo -e "# example\nfoo -bar" | cheat -e somecommand
Too many errors from stdin
Buffer written to ~/.config/cheat/cheatsheets/personal/somecommand.save
failed to edit cheatsheet: exit status 1

$ cheat -e somecommand < echo "snippet"
Too many errors from stdin
Buffer written to ~/.config/cheat/cheatsheets/personal/somecommand.save.1
failed to edit cheatsheet: exit status 1

It would be nice on some occasions to avoid the editor and pipe some
text directly to cheat via a pipe. In other words it would be nice if

• $ echo -e "# example\nfoo -bar" | cheat -e somecommand
• cheat -e somecommand < echo "snippet"
  worked.

I know I could do this:

• $ echo -e "# example\nfoo -bar" >> ~/.config/cheat/cheatsheets/personal/somecommand
• $ cat "snippet" >> ~/.config/cheat/cheatsheets/personal/somecommand
  The above feature could do the same, check if there is input on stdin, if so avoid
  the editor and append the stdin input directly to the end of the cheatsheet.

Additional context
Would enable some automation. Scripts could be written that autogenerate cheatsheets,
but I guess scripts can be written that autogenerate cheatsheets directly without cheat.