Update documentation on setting reno's earliest-version (backport Qiskit#15243) (Qiskit#15256)

* Update documentation on setting reno's `earliest-version` (Qiskit#15243)

The important thing for `reno` is that it pulls in _all_ pre-releases in
the given minor cycle.  That doesn't always mean starting at `rc1`;
sometimes we make "beta" preview releases, and we still want to include
release notes that came in before those tags.  If we ever made an
"alpha" tag, we'd want to include that too.

(cherry picked from commit 882e3ca)

* Fix broken release-notes cross-references

---------

Co-authored-by: Jake Lishman <[email protected]>

Author: mergify[bot]

docs/release_notes.rst

@@ -5,9 +5,20 @@ Qiskit |version| release notes
 ==============================
 
 ..
-    These release notes get converted into Markdown files via the infrastructure at https://github.com/Qiskit/documentation, which then gets deployed to https://quantum.cloud.ibm.com/docs/api/qiskit/release-notes. Changes to these release notes will update those release notes the next time the API docs are generated for this version.
+    These release notes get converted into Markdown files via the infrastructure at
+    https://github.com/Qiskit/documentation, which then gets deployed to
+    https://quantum.cloud.ibm.com/docs/api/qiskit/release-notes. Changes to these release notes will
+    update those release notes the next time the API docs are generated for this version.
 
-    `:earliest-version:` should be set to the rc1 release for the current minor release series. For example, the stable/1.1 branch should set it to 1.1.0rc1. If on `main`, set to the prior minor version's rc1, like `1.0.0rc1`.
+    You should set `earliest-version` to:
+
+    * if on a `stable` branch, then the _earliest_ tagged release of the minor series.  For
+      `stable/2.1` this would be `2.1.0rc1`.  For `stable/2.2` this would be `2.2.0b1`.  Typically
+      you should update this as part of making the `x.y.0` "final" release (e.g. when tagging
+      `2.2.0` or `2.3.0`).
+    * if on `main`: it doesn't matter all too much; it just affects how many old release notes
+      are built and tested as part of the release.  It still needs to be a tag reachable on `main`,
+      though, which is typically `rc1` tags.
 
 .. release-notes::
-   :earliest-version: 2.2.0rc1
+   :earliest-version: 2.2.0b1

releasenotes/notes/2.2/cbindgen-usize-to-size_t-544294518fdfcbb0.yaml

@@ -1,11 +1,11 @@
 ---
 upgrade_c:
   - |
-    Most usage of `uintptr_t`` has been changed to ``size_t``. Specifically the following usages have been changed:
+    Most usage of ``uintptr_t`` has been changed to ``size_t``. Specifically the following usages have been changed:
 
-      * :c:member:`QkOpCount::count`
-      * :c:member:`QkOpCounts::len`
-      * :c:member:`QkObsTerm::len`
+      * :c:member:`QkOpCount.count`
+      * :c:member:`QkOpCounts.len`
+      * :c:member:`QkObsTerm.len`
       * The return type of :c:func:`qk_circuit_num_instructions`.
       * The ``index`` argument in :c:func:`qk_circuit_get_instruction`.
       * The ``boundaries`` argument in :c:func:`qk_obs_new`.