Clarify we want UTF-8 input

Fixes #101.

README.md

@@ -1,5 +1,7 @@
-Moar is a pager. It's designed to just do the right thing without any
-configuration:
+Moar is a pager. It reads and displays UTF-8 encoded text from files or
+pipelines.
+
+`moar` is designed to just do the right thing without any configuration:
 
 ![Moar displaying its own source code](screenshot.png)
 

moar.1

@@ -20,6 +20,9 @@ More information and screenshots: https://github.com/walles/moar#readme
 Inside of \fBmoar\fR, press
 .B ?
 to access the built-in help.
+.PP
+Input is expected to be (optionally compressed) UTF-8 text.
+Invalid / unprintable characters are by default rendered as '?'.
 .SH OPTIONS
 Multiple-choice options all have the default value listed first.
 .PP

moar.go

@@ -41,6 +41,8 @@ func printUsage(output io.Writer, flagSet *flag.FlagSet, printCommandline bool)
 	_, _ = fmt.Fprintln(output, "  moar < file")
 	_, _ = fmt.Fprintln(output)
 	_, _ = fmt.Fprintln(output, "Shows file contents. Compressed files will be transparently decompressed.")
+	_, _ = fmt.Fprintln(output, "Input is expected to be (possibly compressed) UTF-8 encoded text. Invalid /")
+	_, _ = fmt.Fprintln(output, "non-printable characters are by default rendered as '?'.")
 	_, _ = fmt.Fprintln(output)
 	_, _ = fmt.Fprintln(output, "More information + source code:")
 	_, _ = fmt.Fprintln(output, "  <https://github.com/walles/moar#readme>")