netshaper: fix grammar and style issues in man page

This patch addresses grammatical errors and style inconsistencies in
the netshaper man page documentation.

Changes:
  - Improve clarity of set command description by restructuring
    awkward parenthetical about id parameter
  - Fix punctuation consistency in scope list formatting
  - Capitalize "ID" in example heading for proper title case
  - Add missing article "the" in color option description (3 instances)
  - Make example descriptions consistent by using present tense
    third person ("Displays", "Removes") to match Example 1

No functional changes. All technical content remains accurate.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David Ahern <dsahern@kernel.org>