git am: add page (#2352)

pages/common/git-am.md

@@ -0,0 +1,16 @@
+# git am
+
+> Apply patch files. Useful when receiving commits via email.
+> See also `git format-patch`, which can generate patch files.
+
+- Apply a patch file:
+
+`git am {{path/to/file.patch}}`
+
+- Abort the process of applying a patch file:
+
+`git am --abort`
+
+- Apply as much of a patch file as possible, saving failed hunks to reject files:
+
+`git am --reject {{path/to/file.patch}}`