add FAQ

doc/index.html

@@ -111,6 +111,37 @@ The options which are hardcoded are:
 You can use <tt>\</tt> or <tt>"</tt> to escape characters in this
 commandline.</dd>
 
+
+<h2>Frequently Asked Questions</h2>
+
+<p>Here are some common complaints:</p>
+
+<ul>
+<li> Writing to an SD card is not generally possible.  Modern Android
+(since about Kit Kat) only allows write access to an SD card through the
+Android Java API, but shell commands usually use Unix APIs (POSIX, C).  I
+don't know a work-around.  Most phones let you write to <tt>/sdcard</tt>,
+but it's actually in the phone's internal memory.
+
+<li> There is no way to update the ctime, mtime, or atime on files in
+<tt>/sdcard</tt>.  Android system generally forces all files created in
+<tt>/sdcard</tt> to be owned by <tt>root</tt>, and regular users can't
+change the mtime/atime of files they don't own.  If you want to
+<tt>rsync</tt> to a phone, consider the <tt>--size-only</tt> option,
+which will prevent checking the contents of files if their size matches
+(not guaranteed to be correct, but faster than verifying each file's
+contents).
+
+<li> "<tt>Not backgrounding</tt>" is just the string that dropbear
+outputs when it isn't asked to <tt>fork()</tt> when it starts up.
+
+<li> If you really must specify which IP to listen on, consider setting
+<b>Port Number</b> to 22 (which will fail and be ignored), and then add
+<tt>-p 192.168.1.123:2222</tt> to <b>Extra Commandline</b>.
+
+</ul>
+
+
 <h2>Change Log</h2>
 
 <ul>