p7zip: add page (#3813)

pages/common/p7zip.md

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+# p7zip
+
+> Wrapper of 7-Zip file archiver with high compression ratio.
+> Internally executes either 7za or 7zr command.
+> More information: <http://p7zip.sourceforge.net>.
+
+- Archive a file, replacing it with a 7zipped compressed version:
+
+`p7zip {{path/to/file}}`
+
+- Archive a file keeping the input file:
+
+`p7zip -k {{path/to/file}}`
+
+- Decompress a file, replacing it with the original uncompressed version:
+
+`p7zip -d {{compressed.ext}}.7z`
+
+- Decompress a file keeping the input file:
+
+`p7zip -d -k {{compressed.ext}}.7z`
+
+- Skip some checks and force compression or decompression:
+
+`p7zip -f {{path/to/file}}`