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

tldr/umask

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# umask
+
+> Manage the read/write/execute permissions that are masked out (i.e. restricted) for newly created files by the user.
+> More information: <https://manned.org/umask>.
+
+- Display the current mask in octal notation:
+
+`umask`
+
+- Display the current mask in symbolic (human-readable) mode:
+
+`umask -S`
+
+- Change the mask symbolically to allow read permission for all users (the rest of the mask bits are unchanged):
+
+`umask {{a+r}}`
+
+- Set the mask (using octal) to restrict no permissions for the file's owner, and restrict all permissions for everyone else:
+
+`umask {{077}}`