Update cheatsheets

pgmenhance

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# pgmenhance
+
+> Edge-enhance a PGM image.
+> See also: `pamedge`.
+> More information: <https://netpbm.sourceforge.net/doc/pgmenhance.html>.
+
+- Edge-enhance a PGM image:
+
+`pgmenhance {{path/to/image.pgm}} > {{path/to/output.pgm}}`
+
+- Specify the level of enhancement:
+
+`pgmenhance -{{1..9}} {{path/to/image.pgm}} > {{path/to/output.pgm}}`