docs: Update to vanity URL for the docs (#4494)

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

README.md

@@ -96,7 +96,7 @@ decisions, etc. Please be aware of our [Code of Conduct](CODE_OF_CONDUCT.md).
 💁 User Documentation
 ---------------------
 
-[OpenImageIO Documentation on ReadTheDocs](https://openimageio.readthedocs.io/)
+[OpenImageIO Documentation](https://docs.openimageio.org)
 is the best place to start if you are interested in how to use OpenImageIO,
 its APIs, its component programs (once they are built). There is also a [PDF
 version](https://readthedocs.org/projects/openimageio/downloads/pdf/latest/).

docs/dev/RELEASING.md

@@ -205,7 +205,7 @@ have a heading added at the top for the *next* version.
      sure new contributors are listed.
    - [SECURITY.md](SECURITY.md): Make sure it accurately reflects the
      status of which branches get updates.
-   - Skim the [user documentation](https://openimageio.readthedocs.io/) to
+   - Skim the [user documentation](https://docs.openimageio.org) to
      ensure it's building correctly and doesn't have any obvious errors,
      especially the parts that describe new features.
 
@@ -366,11 +366,11 @@ Odds and ends to do after the tag is pushed and the announcements are sent:
 - Re-read RELEASING.md and ensure that the instructions match what you
   have done. Update as necessary.
 
-- Go to [readthedocs.org](https://openimageio.readthedocs.io/), and ensure
-  that the new release is built, visible, and is the default release shown
-  (specified in the Admin section). I tend to keep the latest patch of each
-  minor release available for reference indefinitely, but hide the docs for
-  earlier patch releases within that minor release series.
+- Go to [OIIO's docs hosted on readthedocs.org](https://docs.openimageio.org),
+  and ensure that the new release is built, visible, and is the default
+  release shown (specified in the Admin section). I tend to keep the latest
+  patch of each minor release available for reference indefinitely, but hide
+  the docs for earlier patch releases within that minor release series.
 
 - Edit the top-level CMakeList.txt to update the version to the *next*
   anticipated release on the branch, in order to ensure that anybody building

src/doc/Building_the_docs.md

@@ -3,8 +3,8 @@
 
 # Building the OpenImageIO documentation
 
-The main OpenImageIO documentation can be read on [OpenImageIO Documentation
-on ReadTheDocs](https://openimageio.readthedocs.io/).
+The main OpenImageIO documentation can be read on [OpenImageIO
+Documentation](https://docs.openimageio.org).
 
 But sometimes -- such as for developers who are editing the documentation --
 it is helpful to be able to build and preview it locally. These are the steps

src/oiiotool/oiiotool.cpp

@@ -6187,7 +6187,7 @@ print_help_end(Oiiotool& ot, std::ostream& out)
     // same area is this executable, otherwise just point to the copy on
     // GitHub corresponding to our version of the softare.
     print(out, "Full OIIO documentation can be found at\n");
-    print(out, "    https://openimageio.readthedocs.io\n");
+    print(out, "    https://docs.openimageio.org\n");
 }