Updates and corrections to User Guide.

doc/user_guide/en/install-mac.adoc

@@ -1,6 +1,6 @@
 // These instructions are up-to-date for WSJT-X v1.9
 
-*OS X 10.10* and later: Download the file {osx} to your desktop,
+*macOS 10.13* and later: Download the file {osx} to your desktop,
 double-click on it and consult its `ReadMe` file for important
 installation notes.  
 

doc/user_guide/en/introduction.adoc

@@ -16,9 +16,8 @@ making reliable QSOs under weak-signal conditions. They use nearly
 identical message structure and source encoding.  JT65 and QRA64 were
 designed for EME ("`moonbounce`") on the VHF/UHF bands and have also
 proven very effective for worldwide QRP communication on the HF bands.
-QRA64 has a number of advantages over JT65, including better
-performance on the very weakest signals.  We imagine that over time it
-may replace JT65 for EME use.  JT9 was originally designed for the LF,
+QRA64 has some advantages over JT65, including better performance on
+the higher microwave bands.  JT9 was originally designed for the LF,
 MF, and lower HF bands.  Its submode JT9A is 2 dB more sensitive than
 JT65 while using less than 10% of the bandwidth.  JT4 offers a wide
 variety of tone spacings and has proven highly effective for EME on

doc/user_guide/en/system-requirements.adoc

@@ -1,7 +1,7 @@
 // Status=review
 
 - SSB transceiver and antenna 
-- Computer running Windows (XP or later), Linux, or OS X
+- Computer running Windows 7 or later, macOS 10.13 or later, or Linux
 - 1.5 GHz or faster CPU and 200 MB of available memory; faster
 machines are better
 - Monitor with at least 1024 x 780 resolution