bfg: add page (#5984)

pages/common/bfg.md

@@ -0,0 +1,13 @@
+# bfg
+
+> Remove large files or passwords from Git history like git-filter-branch.
+> Note: if your repository is connected to a remote, you will need to force push to it.
+> More information: <https://rtyley.github.io/bfg-repo-cleaner/>.
+
+- Remove a file with sensitive data but leave the latest commit untouched:
+
+`bfg --delete-files {{file_with_sensitive_data}}`
+
+- Remove all text mentioned in the specified file wherever it can be found in the repository's history:
+
+`bfg --replace-text {{path/to/file.txt}}`