Add migration guide for method get_all_records

Add the new section in the v6 migration guide about
the method `Worksheet.get_all_records` to allow users
to migrate from previous method signature to the new one.

closes #1376

Signed-off-by: Alexandre Lavigne <[email protected]>

README.md

@@ -88,6 +88,41 @@ file.sheet1.update_tab_color(tab_color)
 + age = spreadsheet.get_lastUpdateTime()
 ```
 
+### Removed method `Worksheet.get_records`
+
+The method `Worksheet.get_records()` has been removed.
+The function `utils.to_records` has been added.
+
+It takes hearder row, a matrix values and build the records from them.
+
+### Simplify method `Worksheet.get_all_records`
+
+v6 simplified the method `Worksheet.get_all_records`, it does not accept a bounded ranges of rows for
+the values to fill the records. The below arguments have been remove from the method signature:
+
+- first_index
+- last_index
+
+It now uses the function `utils.to_records`.
+
+Update the method signature as follow:
+
+```diff
+  get_all_records(
+      empty2zero=False,
+      head=1,
+-     first_index=None,
+-     last_index=None,
+      default_blank="",
+      allow_underscores_in_numeric_literals=False,
+      numericise_ignore=[],
+      value_render_option=None,
+      expected_headers=None,
+  )
+```
+
+In order to achieve the previous behavior one case use the new function `utils.to_records` by manually providing the headers and the values.
+
 ### Silence warnings
 
 In version 5 there are many warnings to mark deprecated feature/functions/methods.