Tiny fixes for the documentation (#594)

* Add a missing period
* The code of conduct is mentioned in the section below
* GMT 6 is already released

Co-authored-by: Wei Ji <23487320+weiji14@users.noreply.github.com>

Author: seisman

README.rst

@@ -45,7 +45,7 @@ Disclaimer
 All of the API (functions/classes/interfaces) is subject to change until we reach v1.0.0
 as per the `semantic versioning specification <https://semver.org/spec/v2.0.0.html>`__.
 There may be non-backward compatible changes as we experiment with new design ideas and
-implement new features. **This is not a finished product, use with caution**
+implement new features. **This is not a finished product, use with caution.**
 
 We welcome any feedback and ideas!
 Let us know by submitting
@@ -85,9 +85,6 @@ Contacting Us
   open issue or pull request.
 * We have a `Discourse forum <https://forum.generic-mapping-tools.org>`__
   where you can ask questions and leave comments.
-* This project is released with a `Contributor Code of Conduct
-  <https://github.com/GenericMappingTools/pygmt/blob/master/CODE_OF_CONDUCT.md>`__.
-  By participating in this project you agree to abide by its terms.
 
 
 Contributing

examples/tutorials/first-figure.py

@@ -66,8 +66,7 @@
 #
 # You’ll probably have noticed several things that are different from classic
 # command-line GMT. Many of these changes reflect the new GMT modern execution mode that
-# will be part of the future 6.0 release. A few are PyGMT exclusive (like the
-# ``savefig`` method).
+# are part of GMT 6. A few are PyGMT exclusive (like the ``savefig`` method).
 #
 # 1. The name of method is ``coast`` instead of ``pscoast``. As a general rule, all
 #    ``ps*`` modules had their ``ps`` prefix removed. The exceptions are: