Update documentation for middlemouse panning in presentation mode

doc/pho.1

@@ -31,7 +31,8 @@ of your dog, etc.
 .TP
 \fB\-p\fR
 "Presentation mode": display in full screen mode with a black background
-(if the window manager allows it).
+(if the window manager allows it). In presentation mode, if you zoom in
+and need to move (pan) in the image, drag with the middle mouse button.
 .TP
 \fB\-P\fR
 Force non-presentation mode (e.g. if you set PHO_ARGS=-p).

doc/pho.html

@@ -38,7 +38,7 @@ <h1>pho: View and annotate multiple images</h1>
 has its own comment.
 
 <p>
-There's also a new slideshow mode, where you specify the interval in seconds
+There's also a slideshow mode, where you specify the interval in seconds
 (e.g. pho -p -s5 for a 5-second delay between images).
 You can use this for a screensaver, or just to go through slides
 automatically. Hitting the spacebar cancels slideshow mode.
@@ -153,6 +153,15 @@ <h2>How to use pho</h2>
 <dt>q                       <dd>Quit.
 </dl>
 
+<p>
+Presentation mode makes pho fullscreen; it also enables mouse bindings,
+where dragging with the middle mouse button will pan in the image.
+By default, pho will scale images to fit the screen, but if you
+zoom in, either with f (full size) or + (double size), panning
+is useful. (In non-presentation mode, you can use your window manager
+to move the window.)
+
+<p>
 pho will remember the correct (last shown) rotation for each image.
 When it exits (either because the last image was viewed or because
 the user typed q), it will print out the images that need to be

pho.c

@@ -780,11 +780,14 @@ void VerboseHelp()
     printf("/\tHalf size\n");
     printf("<kp>-\tHalf size\n");
     printf("i\tShow/hide info dialog\n");
-    printf("o\nChange the working file set (add files or make a new list)\n");
+    printf("o\tChange the working file set (add files or make a new list)\n");
     printf("g\tRun gimp on the current image\n");
     printf("\t(or set PHO_REMOTE to an alternate command)\n");
     printf("q\tQuit\n");
     printf("<esc>\tQuit (or hide a dialog, if one is showing)\n");
+    printf("\n");
+    printf("Pho mouse bindings\n");
+    printf("In presentation mode: drag with middlemouse to pan/move.\n");
     exit(1);
 }