git-fast-export: add page (#18490)

Co-authored-by: Managor <42655600+Managor@users.noreply.github.com>
Co-authored-by: Lena Pastwa <126529524+acuteenvy@users.noreply.github.com>

pages/common/git-fast-export.md

@@ -0,0 +1,24 @@
+# git fast-export
+
+> Exports the contents and history of a Git repository in a streamable, plain-text format.
+> More information: <https://manned.org/git-fast-export>.
+
+- Export the entire Git repository history to `stdout`:
+
+`git fast-export --all`
+
+- Export the entire repository to a file:
+
+`git fast-export --all > {{path/to/file}}`
+
+- Export a specific branch only:
+
+`git fast-export {{main}}`
+
+- Export with `progress` statements every `n` objects (for showing progress during `git fast-import`):
+
+`git fast-export --progress {{n}} --all > {{path/to/file}}`
+
+- Export only a specific subdirectory’s history:
+
+`git fast-export --all -- {{path/to/directory}} > {{path/to/file}}`