Add missing spaces around back-quoted block

[robertjank]

Project: Build a LAMP Web Server with WordPress
Language: de-DE
File: step_6.md, line 11

This line starts with the sentence

Falls du dich fragst, `.tar.gz`steht für 'gzip-compressed tar archive' (also gzip-komprimiertes Tar-Archiv).
It would be nice if NTTT could add a space between `.tar.gz` and steht.

Note that there are some complications:

• No space after a back-quoted block if it is followed by punctuation, like a period or a comma.
• No space before a back-quoted block if it is at the beginning of a line.