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

tldr/osx/base64

@@ -0,0 +1,25 @@
+---
+syntax: markdown
+tags: [tldr, osx]
+source: https://github.com/tldr-pages/tldr.git
+---
+# base64
+
+> Encode and decode using Base64 representation.
+> More information: <https://keith.github.io/xcode-man-pages/base64.1.html>.
+
+- Encode a file:
+
+`base64 --input={{plain_file}}`
+
+- Decode a file:
+
+`base64 --decode --input={{base64_file}}`
+
+- Encode from `stdin`:
+
+`echo -n "{{plain_text}}" | base64`
+
+- Decode from `stdin`:
+
+`echo -n {{base64_text}} | base64 --decode`