Update base_chart.md docs

repo_files/documentations/base_chart.md

@@ -67,7 +67,7 @@
 |propName|Description|default value|
 |:-------|:----------|:------------|
 |color|determines the color of line|Colors.black|
-|gradient|gradient of the line|null|
+|gradient|gradient of the line (you have to provide either `color` or `gradient`|null|
 |strokeWidth|determines the stroke width of the line|2|
 |dashArray|A circular array of dash offsets and lengths. For example, the array `[5, 10]` would result in dashes 5 pixels long followed by blank spaces 10 pixels long.  The array `[5, 10, 5]` would result in a 5 pixel dash, a 10 pixel gap, a 5 pixel dash, a 5 pixel gap, a 10 pixel dash, etc.|null|
 
@@ -135,6 +135,7 @@ Base class for all supported touch/pointer events.
 |:-------|:----------|:------------|
 |y|draw straight line from left to right of the chart with dynamic y value|null|
 |color|color of the line|Colors.black|
+|gradient|gradient of the line (you have to provide either `color` or `gradient`|null|
 |strokeWidth|strokeWidth of the line|2|
 |strokeCap|strokeCap of the line,e.g. Setting to StrokeCap.round will draw the tow ends of line rounded. NOTE: this might not work on dash lines.|StrokeCap.butt|
 |image|image to annotate the line. the Future must be complete at the time this is received by the chart|null|
@@ -146,6 +147,7 @@ Base class for all supported touch/pointer events.
 |:-------|:----------|:------------|
 |x|draw straight line from bottom to top of the chart with dynamic x value|null|
 |color|color of the line|Colors.black|
+|gradient|gradient of the line (you have to provide either `color` or `gradient`|null|
 |strokeWidth|strokeWidth of the line|2|
 |strokeCap|strokeCap of the line,e.g. Setting to StrokeCap.round will draw the tow ends of line rounded. NOTE: this might not work on dash lines.|StrokeCap.butt|
 |image|image to annotate the line. the Future must be complete at the time this is received by the chart|null|