clarify difference between value and qcol options

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@56039 15284696-431f-4ddb-bdfa-cd5b030d7da7

scripts/v.db.update/v.db.update.html

@@ -1,8 +1,8 @@
 <h2>DESCRIPTION</h2>
 
 <em>v.db.update</em> assigns a new value to a column in the
-attribute table connected to a given map. Alternatively, values can be
-copied from another column in the table.
+attribute table connected to a given map. The <em>value</em> parameter allows updating with a literal value. Alternatively, with the <em>qcol</em> parameter values can be
+copied from another column in the table or be the result of a combination or transformation of other columns.
 
 
 <h2>NOTES</h2>

scripts/v.db.update/v.db.update.py

@@ -33,12 +33,12 @@
 #%option
 #% key: value
 #% type: string
-#% description: Value to update the column with, can be (combination of) other column(s)
+#% description: Literal value to update the column with
 #% required: no
 #%end
 #%option G_OPT_DB_COLUMN
 #% key: qcolumn
-#% description: Name of attribute column to query
+#% description: Name of other attribute column to query, can be combination of columns (e.g. co1+col2)
 #%end
 #%option G_OPT_DB_WHERE
 #%end