stdbuf: add page (#2618)

* stdbuf: add page

pages/common/stdbuf.md

@@ -0,0 +1,15 @@
+# stdbuf
+
+> Run a command with modified buffering operations for its standard streams.
+
+- Change the standard input buffer size to 512 KiB:
+
+`stderr --input={{512K}} {{command}}`
+
+- Change the standard output buffer to line-buffered:
+
+`stdbuf --output={{L}} {{command}}`
+
+- Change the standard error buffer to unbuffered:
+
+`stdbuf --error={{0}} {{command}}`