Detail the features

README.md

@@ -48,6 +48,8 @@ Collection of ASCII art from various sources:
 
 ## Features
 
+All the features of the dataset are textual:
+
 ```python
 datasets.Features({
     'caption': datasets.features.Value(dtype='string'),
@@ -57,6 +59,32 @@ datasets.Features({
     'chartypes': datasets.features.Value(dtype='string'),})
 ```
 
+- `caption`:
+    - a brief description of the "image"
+    - for example `"Undertale Sans full body"`
+    - can be empty
+- `content`:
+    - the actual ASCII art, in UTF-8 encoding
+    - for example `"(╯°□°)╯︵ ┻━┻ FLIP THAT TABLE.\r\n┻━┻ ︵ ヽ(°□°ヽ) FLIP THIS TABLE."`
+    - is never empty
+- `labels`:
+    - a list of tags, separated by commas
+    - the set of tags depends on the dataset
+    - for example `"Cartoons,Smurfs"`
+    - can be empty
+- `charsets`:
+    - the [Unicode sections][unicode-nameslist] of the characters in the AA
+    - for example `"Braille Patterns,ASCII C0"`
+    - "C0 Controls and Basic Latin" is renamed "ASCII C0"
+    - "C1 Controls and Latin-1 Supplement" is renamed "ASCII C1"
+    - is never empty
+- `chartypes`:
+    - the [types of characters][wiki-category] in the AA
+    - for example `"Punctuations,Others,Symbols,Letters"`
+    - is never empty
+
 [github-scrapscii]: https://github.com/apehex/scrapscii/
 [source-asciiart]: https://www.asciiart.eu/
 [source-twitchquotes]: https://www.twitchquotes.com/
+[unicode-nameslist]: https://www.unicode.org/charts/nameslist/
+[wiki-category]: https://en.wikipedia.org/wiki/Unicode_character_property#General_Category