update doxygen for t_chan

Author: soheilshahrouz

libs/libarchfpga/src/physical_types.h

@@ -1541,9 +1541,11 @@ enum class e_stat {
 };
 
 /// @brief Parameters describing a channel distribution.
+/// @note  If detailed routing is performed, only a uniform (all channels in a given direction are the same width)
+/// distribution is supported.
 struct t_chan {
     e_stat type;  ///< Distribution type
-    float peak;   ///< Peak value
+    float peak;   ///< Peak value. For a UNIFORM distribution, this is the value for all channels (in a given direction).
     float width;  ///< Standard deviation (Gaussian)
     float xpeak;  ///< Peak location (Gaussian)
     float dc;     ///< DC offset (Gaussian, pulse)