zgrep: add page (#4131)

Co-authored-by: Zlatan Vasović <zlatanvasovic@gmail.com>

pages/linux/zgrep.md

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+# zgrep
+
+> Grep text patterns from files within compressed file (equivalent to grep -Z).
+
+- Grep a pattern in a compressed file (case-sensitive):
+
+`zgrep {{pattern}} {{path/to/compressed/file}}`
+
+- Grep a pattern in a compressed file (case-insensitive):
+
+`zgrep -i {{pattern}} {{path/to/compressed/file}}`
+
+- Output count of lines containing matched pattern in a compressed file:
+
+`zgrep -c {{pattern}} {{path/to/compressed/file}}`
+
+- Display the lines which don’t have the pattern present (Invert the search function):
+
+`zgrep -v {{pattern}} {{path/to/compressed/file}}`
+
+- Grep a compressed file for multiple patterns:
+
+`zgrep -e "{{pattern_1}}" -e "{{pattern_2}}" {{path/to/compressed/file}}`
+
+- Use extended regular expressions (supporting `?`, `+`, `{}`, `()` and `|`):
+
+`zgrep -E {{^regex$}} {{path/to/file}}`
+
+- Print 3 lines of [C]ontext around, [B]efore, or [A]fter each match:
+
+`zgrep -{{C|B|A}} {{3}} {{pattern}} {{path/to/compressed/file}}`