eqn, grap, groff, pic, tbl, troff: add page (#6868)

pages/common/grap.md

@@ -0,0 +1,13 @@
+# grap
+
+> A charting preprocessor for the groff (GNU Troff) document formatting system.
+> See also `pic` and `groff`.
+> More information: <https://manned.org/grap>.
+
+- Process a `grap` file and save the output file for future processing with `pic` and `groff`:
+
+`grap {{path/to/input.grap}} > {{path/to/output.pic}}`
+
+- Typeset a `grap` file to PDF using the [me] macro package, saving the output to a file:
+
+`grap {{path/to/input.grap}} | pic -T {{pdf}} | groff -{{me}} -T {{pdf}} > {{path/to/output.pdf}}`