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

tldr/export

@@ -0,0 +1,17 @@
+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# export
+
+> Export shell variables to child processes.
+> More information: <https://manned.org/export.1posix>.
+
+- Set an environment variable:
+
+`export {{VARIABLE}}={{value}}`
+
+- Append a pathname to the environment variable `PATH`:
+
+`export PATH=$PATH:{{path/to/append}}`