Define features explicitly in the dataset card

Define features explicitly in the dataset card, so they are not inferred.

Note that the features are inferred from the first samples. Therefore, if subsequent samples have features different from the inferred ones, an error is raised.

Fix #8.

README.md

@@ -1,5 +1,51 @@
 ---
 license: cc-by-4.0
+dataset_info:
+  features:
+  - name: bff_contained_ngram_count_before_dedupe
+    dtype: int64
+  - name: language_id_whole_page_fasttext
+    struct:
+    - name: en
+      dtype: float64
+  - name: metadata
+    struct:
+    - name: Content-Length
+      dtype: string
+    - name: Content-Type
+      dtype: string
+    - name: WARC-Block-Digest
+      dtype: string
+    - name: WARC-Concurrent-To
+      dtype: string
+    - name: WARC-Date
+      dtype: timestamp[s]
+    - name: WARC-IP-Address
+      dtype: string
+    - name: WARC-Identified-Payload-Type
+      dtype: string
+    - name: WARC-Payload-Digest
+      dtype: string
+    - name: WARC-Record-ID
+      dtype: string
+    - name: WARC-Target-URI
+      dtype: string
+    - name: WARC-Type
+      dtype: string
+    - name: WARC-Warcinfo-ID
+      dtype: string
+    - name: WARC-Truncated
+      dtype: string
+  - name: previous_word_count
+    dtype: int64
+  - name: text
+    dtype: string
+  - name: url
+    dtype: string
+  - name: warcinfo
+    dtype: string
+  - name: fasttext_openhermes_reddit_eli5_vs_rw_v2_bigram_200k_train_prob
+    dtype: float64
 ---
 ## DCLM-baseline 
 DCLM-baseline is a 4T token / 3B document pretraining dataset that achieves strong performance on language model benchmarks.