f3write: add page

pages/common/f3write.md

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+# f3write
+
+> Fill a drive out with .h2w files to test its real capacity.
+> See also `f3read`, `f3probe`, `f3fix`.
+> More information: <http://oss.digirati.com.br/f3/>.
+
+- Write test files to a given directory, filling the drive:
+
+`f3write {{path/to/mount_point}}`
+
+- Limit the write speed:
+
+`f3write --max-write-rate={{kb_per_second}} {{path/to/mount_point}}`
+