Starting work on updating use of Echo mode in the User Guide.

doc/user_guide/en/introduction.adoc

@@ -70,7 +70,8 @@ provides a mapping facility, archival storage, and many other
 features.
 
 *Echo* mode allows you to detect and measure your own station's echoes
-from the moon, even if they are far below the audible threshold.
+from the moon and to make other measurements useful for optimizing
+your EME station's performance.
 
 _WSJT-X_ provides spectral displays for receiver passbands as wide as
 5 kHz, flexible rig control for nearly all modern radios used by

doc/user_guide/en/new_features.adoc

@@ -15,10 +15,11 @@ that station.
 of situations with available _a priori_ (AP) information.
 
 - *Echo* mode now offers a *Clear Avg* button and produces reliable
-measurements of SNR even when Doppler spread is large.  The *Measure*
-function can be used to measure SNR for a received unmodulated carrier
--- for example, a key-down test signal emitted by another station and
-reflected from the Moon.
+measurements of SNR even when Doppler spread is large.  Its *Monitor*
+function can be used to measure SNR for a received unmodulated
+carrier such as a key-down test signal emitted by another station and
+reflected from the Moon, and to measure Sun, Moon, and ground noise as
+aids for optimizing an EME station's performance.
 
 - New buttons on the main window allow quick changes between modes
 FT4, FT8, MSK144, Q65, and JT65.  Another new button allows toggling