Update CODE_OF_CONDUCT.md

Author: BobinMathew

CODE_OF_CONDUCT.md

@@ -1,3 +1,6 @@
 # pystac Community Code of Conduct
 
+## Our Pledge
+In the interest of fostering an open and welcoming environment, we as contributors and maintainers pledge to making participation in our project and our community a harassment-free experience for everyone, regardless of age, body size, disability, ethnicity, sex characteristics, gender identity and expression, level of experience, education, socio-economic status, nationality, personal appearance, race, religion, or sexual identity and orientation.
+
 pystac follows the [STAC spec Code of Conduct](https://github.com/radiantearth/stac-spec/blob/master/CODE_OF_CONDUCT.md).