indent: add page (#4443)

pages/common/indent.md

@@ -0,0 +1,16 @@
+# indent
+
+> Change the appearance of a C/C++ program by inserting or deleting whitespace.
+> More information: <https://www.gnu.org/software/indent/>.
+
+- Format C/C++ source according to the Linux style guide, automatically back up the original files, and replace with the indented versions:
+
+`indent --linux-style {{path/to/source.c}} {{path/to/another_source.c}}`
+
+- Format C/C++ source according to the GNU style, saving the indented version to a different file:
+
+`indent --gnu-style {{path/to/source.c}} -o {{path/to/indented_source.c}}`
+
+- Format C/C++ source according to the style of Kernigan & Ritchie (K&R), no tabs, 3 spaces per indent, and wrap lines at 120 characters:
+
+`indent --k-and-r-style --indent-level3 --no-tabs --line-length120  {{path/to/source.c}} -o {{path/to/indented_source.c}}`