git-clear: add page (#6614)

pages/common/git-clear.md

@@ -0,0 +1,9 @@
+# git clear
+
+> Clear a Git working directory as if it was freshly cloned with the current branch including files in `.gitignore`.
+> Part of `git-extras`.
+> More information: <https://github.com/tj/git-extras/blob/master/Commands.md#git-clear>.
+
+- Reset all tracked files and delete all untracked files even if they are included in the `.gitignore`:
+
+`git clear`