feat: adding citation.cff and address reviews

CITATION.cff

@@ -0,0 +1,17 @@
+cff-version: 1.2.0
+title: >-
+  Substrait: Cross-Language Serialization for Relational
+  Algebra
+message: >-
+  If you use this software, please cite it using the
+  metadata from this file.
+type: software
+authors:
+  - given-names: substrait-io
+identifiers:
+  - type: url
+    value: 'https://github.com/substrait-io/substrait'
+repository-code: 'https://github.com/substrait-io/substrait'
+url: 'https://substrait.io/'
+license: Apache-2.0
+date-released: '2021-09-01'

site/docs/community/index.md

@@ -39,10 +39,12 @@ If you use Substrait in your research, please cite it using the following BibTeX
 @misc{substrait,
   author = {substrait-io},
   title = {Substrait: Cross-Language Serialization for Relational Algebra},
-  year = {2021-September-01},
+  year = {2021},
+  month = {8},
+  day = {31},
   publisher = {GitHub},
   journal = {GitHub repository},
-  howpublished = {\url{https://github.com/substrait-io/substrait}},
+  howpublished = {\url{https://github.com/substrait-io/substrait}}
 }
 ```