>> update documentation

README.md

@@ -37,3 +37,5 @@ See [Infrequently Asked Questions](./iaq.md) for unimportant information.
 5. mmv: <https://github.com/rrthomas/mmv>
 6. PathShortener: <https://github.com/ElectricRCAircraftGuy/eRCaGuy_PathShortener>
 7. fuseblk-filename-fixer: <https://github.com/DDR0/fuseblk-filename-fixer>
+8. POSIX Portable Filename Set (see section 3.265): 
+   <https://pubs.opengroup.org/onlinepubs/9799919799/>

main.go

@@ -262,6 +262,8 @@ func printHelp() {
    -h,--help
    -v,--version
    -r,--recurse DIRECTORY
+   -n,--dry-run
+   -p,--portable
 
 `);
 }

man.md

@@ -32,6 +32,11 @@ includes DIRECTORY itself.
 Causes Owl to just print a representation of what would be done without 
 actually renaming any files.
 
+### -p,\-\-portable
+Restrict characters to ones in the POSIX Portable Filename Character Set 
+(see <https://pubs.opengroup.org/onlinepubs/9799919799/>, section 3.265) 
+instead of FAT compatible ones.
+
 ### -v, \-\-version
 Show version information.