filewriter v2 docs: Update type of AXISNAME fields in data

See PR on github:
nexusformat/definitions#1246

filewriter_v2/README.md

@@ -185,9 +185,9 @@ Describes the plottable data and related dimension scales. Please also refer to
 | [@channel_indices](https://manual.nexusformat.org/classes/base_classes/NXdata.html#nxdata-axisname-indices-attribute) | NX_INT | Indicates the dependency relationship of the `channel` field with a dimension of the data, in this case `1`.
 | [@signal](https://manual.nexusformat.org/classes/base_classes/NXdata.html#nxdata-signal-attribute) | NX_CHAR | Declares which field is the default to be plotted, `"data"`. |
 | @default_slice | NX_CHAR_OR_NUMBER | Defines which slice of data should be shown in a plot by default. |
-| [image_id](https://manual.nexusformat.org/classes/base_classes/NXdata.html#nxdata-axisname-field) | NX_NUMBER[] | Dimension scale defining the axis `image_id` of the data, typically this is `[1, ..., nP]`. |
-| [start_time](https://manual.nexusformat.org/classes/base_classes/NXdata.html#nxdata-axisname-field) | NX_NUMBER[] | Dimension scale defining the axis `start_time` of the data. These are the relative start times for all images with absolute reference `/entry/start_time`. |
-| [channel](https://manual.nexusformat.org/classes/base_classes/NXdata.html#nxdata-axisname-field) | NX_CHAR[][^2] | Dimension scale defining the axis `channel` of the data. These are the enabled channels, for example `["threshold_1", "threshold_2", "difference"]`. |
+| [image_id](https://manual.nexusformat.org/classes/base_classes/NXdata.html#nxdata-axisname-field) | NX_CHAR_OR_NUMBER[] | Dimension scale defining the axis `image_id` of the data, typically this is `[1, ..., nP]`. |
+| [start_time](https://manual.nexusformat.org/classes/base_classes/NXdata.html#nxdata-axisname-field) | NX_CHAR_OR_NUMBER[] | Dimension scale defining the axis `start_time` of the data. These are the relative start times for all images with absolute reference `/entry/start_time`. |
+| [channel](https://manual.nexusformat.org/classes/base_classes/NXdata.html#nxdata-axisname-field) | NX_CHAR_OR_NUMBER[][^2] | Dimension scale defining the axis `channel` of the data. These are the enabled channels, for example `["threshold_1", "threshold_2", "difference"]`. |
 | [data](https://manual.nexusformat.org/classes/applications/NXmx.html#nxmx-entry-data-data-field) | NX_NUMBER[nP,nC,i,j] | The image data.<br> **Note:** Files in V2 format always have only one `"/entry/data/data"` dataset, even in case `nimages_per_file` is greater than `0`. This is because it is a [Virtual Dataset](https://portal.hdfgroup.org/display/HDF5/Virtual+Dataset++-+VDS). |
 
 ## [/entry/instrument](https://manual.nexusformat.org/classes/applications/NXmx.html#nxmx-entry-instrument-group)