Update cheatsheets

pnmtosgi

@@ -0,0 +1,21 @@
+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# pnmtosgi
+
+> Convert a PNM file to an SGI image file.
+> More information: <https://netpbm.sourceforge.net/doc/pnmtosgi.html>.
+
+- Convert a PNM image to an SGI image:
+
+`pnmtosgi {{path/to/input.pnm}} > {{path/to/output.sgi}}`
+
+- Disable or enable compression:
+
+`pnmtosgi -{{verbatim|rle}} {{path/to/input.pnm}} > {{path/to/output.sgi}}`
+
+- Write the specified string into the SGI image header's `imagename` field:
+
+`pnmtosgi -imagename {{string}} {{path/to/input.pnm}} > {{path/to/output.sgi}}`