gemtopbm, gemtopnm, pamtotga, ppmtotga, tgatoppm: add pages (#11402)

* gemtopbm, gemtopnm, pamtotga, ppmtotga, tgatoppm: add pages

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Co-authored-by: Sebastiaan Speck <12570668+sebastiaanspeck@users.noreply.github.com>

pages/common/tgatoppm.md

@@ -0,0 +1,20 @@
+# tgatoppm
+
+> Convert a TrueVision Targa file to a Netpbm image.
+> More information: <https://netpbm.sourceforge.net/doc/tgatoppm.html>.
+
+- Convert a TrueVision Targa file to a PPM image:
+
+`tgatoppm {{path/to/file.tga}} > {{path/to/output.ppm}}`
+
+- Dump information from the TGA header to `stdout`:
+
+`tgatoppm --headerdump {{path/to/file.tga}} > {{path/to/output.ppm}}`
+
+- Write the transparency channel values of the input image to the specified file:
+
+`tgatoppm --alphaout {{path/to/transparency_file.pgm}} {{path/to/file.tga}} > {{path/to/output.ppm}}`
+
+- Display version:
+
+`tgatoppm -version`