bg: add page (#911)

pages/common/bg.md

@@ -0,0 +1,11 @@
+# bg
+
+> Resumes suspended jobs and keeps them running in the background.
+
+- Resume most recently suspended background job running in the background:
+
+`bg`
+
+- Resume a specific job running in the background:
+
+`bg {{job_id}}`