basenc: add page (#10164)

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Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

pages/common/basenc.md

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+# basenc
+
+> Encode or decode file or standard input using a specified encoding, to standard output.
+> More information: <https://www.gnu.org/software/coreutils/basenc>.
+
+- Encode a file with base64 encoding:
+
+`basenc --base64 {{path/to/file}}`
+
+- Decode a file with base64 encoding:
+
+`basenc --decode --base64 {{path/to/file}}`
+
+- Encode from `stdin` with base32 encoding with 42 columns:
+
+`{{command}} | basenc --base32 -w42`
+
+- Encode from `stdin` with base32 encoding:
+
+`{{command}} | basenc --base32`