img2txt: add page (#9597)

* img2txt: add page

* img2txt: fix build error

* Update pages/linux/img2txt.md

* img2txt: accepted suggestions

pages/linux/img2txt.md

@@ -0,0 +1,24 @@
+# img2txt
+
+> Convert images to colour ASCII characters and output them to text-based coloured files.
+> More information: <https://manned.org/img2txt>.
+
+- Set output column count to a specific value:
+
+`img2txt --width={{10}}`
+
+- Set output line count to a specific value:
+
+`img2txt --height={{5}}`
+
+- Set output font width to a specific value:
+
+`img2txt --font-width={{12}}`
+
+- Set output font height to a specific value:
+
+`img2txt --font-height={{14}}`
+
+- Set image brightness to a specific value:
+
+`img2txt --brightness={{2}}`