Prepare for a1 release of v2 (#296)

(This should have in been in the alpha 1 release)

README fixes

Set version number to 2.0



* Prepare for a1 release of v2

* Add link to documentation

* miniscule comment fixes

---------

Co-authored-by: Laurence Lundblade <lgl@securitytheory.com>
diff --git a/doc/mainpage.dox b/doc/mainpage.dox
index db8054c..befe158 100644
--- a/doc/mainpage.dox
+++ b/doc/mainpage.dox
@@ -1,6 +1,10 @@
 /*! @mainpage QCBOR Documentation
 
-QCBOR is available for download @ref https://github.com/laurencelundblade/QCBOR "here on GitHub"
+QCBOR can be downloaded from its [GitHub repository](https://github.com/laurencelundblade/QCBOR).
+This documentation corresponds to QCBOR v2, currently in its alpha release
+phase. While much of the content also applies to v1 -- which is stable,
+commercially suitable, and compatible with v2 -- it's important to note that
+v2 introduces new features and APIs not available in v1.
 
 @par Table of Contents
 
@@ -18,10 +22,6 @@
    - Tag decode functions: @ref inc/qcbor/qcbor_tag_decode.h "qcbor_tag_decode.h"
    - Number decode functions: @ref inc/qcbor/qcbor_number_decode.h "qcbor_number_decode.h"
 
-Note:
-- This is for QCBOR v2, but v1 is largely compatible
-- the API Reference is largely complete, the subject matter below is partial
-
 Subject Matter:
 - @ref Overview "QCBOR overview and implementation limits"
 - @ref Building "Building QCBOR with make and cmake"