wdiff: add page (#12507)

pages/common/wdiff.md

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+# wdiff
+
+> Display word differences between text files.
+> More information: <https://www.gnu.org/software/wdiff/>.
+
+- Compare two files:
+
+`wdiff {{path/to/file1}} {{path/to/file2}}`
+
+- Ignore case when comparing:
+
+`wdiff --ignore-case {{path/to/file1}} {{path/to/file2}}`
+
+- Display how many words are deleted, inserted or replaced:
+
+`wdiff --statistics {{path/to/file1}} {{path/to/file2}}`