fix(markLine): add missing symbolOffset option for markLine (apache…

…/echarts#20483)

en/option/partial/mark-line.md

@@ -19,6 +19,21 @@ Symbol size at the two ends of the mark line. It can be an array for two ends, o
 
 **Attention: ** You cannot assign width and height separately as normal `symbolSize`.
 
+##${prefix} symbolOffset(number|string|Array)
+
+Offset of symbol relative to original position. It can be an array for two ends, or assigned separately. If you want to set specific horizontal/vertical offset for single end, you can set it as a 2d array. For example,
+
+```js
+symbolOffset: [
+    [-10, 20],    // offset of starting symbol
+    ['50%', 100]  // offset of ending symbol
+]
+```
+
+{{ use: partial-version(
+    version = "5.1.0"
+) }}
+
 ##${prefix} precision(number) = 2
 
 Precision of marking line value, which is useful when displaying average value mark line.

zh/option/partial/mark-line.md

@@ -19,6 +19,21 @@
 
 **注意：** 这里无法像一般的 `symbolSize` 那样通过数组分别指定高宽。
 
+##${prefix} symbolOffset(number|string|Array)
+
+标线两端的标记相对于原本位置的偏移，可以是一个数组分别指定两端，也可以是单个统一指定。如果希望单独指定两端标记的水平/垂直偏移，也可以是一个二维数组，每个元素为单个标记的偏移量，例：
+
+```js
+symbolOffset: [
+    [-10, 20],    // 起始标记偏移
+    ['50%', 100]  // 结束标记偏移
+]
+```
+
+{{ use: partial-version(
+    version = "5.1.0"
+) }}
+
 ##${prefix} precision(number) = 2
 
 标线数值的精度，在显示平均值线的时候有用。