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

tldr/join

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# join
+
+> Join lines of two sorted files on a common field.
+> More information: <https://www.gnu.org/software/coreutils/join>.
+
+- Join two files on the first (default) field:
+
+`join {{path/to/file1}} {{path/to/file2}}`
+
+- Join two files using a comma (instead of a space) as the field separator:
+
+`join -t {{','}} {{path/to/file1}} {{path/to/file2}}`
+
+- Join field3 of file1 with field1 of file2:
+
+`join -1 {{3}} -2 {{1}} {{path/to/file1}} {{path/to/file2}}`
+
+- Produce a line for each unpairable line for file1:
+
+`join -a {{1}} {{path/to/file1}} {{path/to/file2}}`
+
+- Join a file from `stdin`:
+
+`cat {{path/to/file1}} | join - {{path/to/file2}}`