Move pages under tldr, lint run.sh, update docs

tldr/combine

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# combine
+
+> Perform set operations on lines of two files.
+> The order of the output lines is determined by the order of the lines in the first file.
+> See also: `diff`.
+> More information: <https://joeyh.name/code/moreutils/>.
+
+- Output lines that are in both specified files:
+
+`combine {{path/to/file1}} and {{path/to/file2}}`
+
+- Output lines that are in the first but not in the second file:
+
+`combine {{path/to/file1}} not {{path/to/file2}}`
+
+- Output lines that in are in either of the specified files:
+
+`combine {{path/to/file1}} or {{path/to/file2}}`
+
+- Output lines that are in exactly one of the specified files:
+
+`combine {{path/to/file1}} xor {{path/to/file2}}`