mention osgeo4w qt6 packages (implements #829)

Author: jef-n

content/resources/installation-guide/index.md

@@ -38,7 +38,7 @@ Standalone installers include everything QGIS needs in a single download. Once y
 |Long Term Release|{{< param "ltrrelease" >}} {{< param "ltrcodename" >}} {{< param "ltrnote" >}}|[Installer]({{< param "ltr_msi">}}) [Checksum]({{< param "ltr_sha">}})|
 |Development|{{< param "devversion" >}} master|[Weekly snapshots]({{< param "weekly_msi">}})|
 
-The weekly snapshots of the nightly qgis-dev package of OSGeo4W are for users that cannot use OSGeo4W (see below) for some reason or just prefer standalone installers. In the feature freeze phase, these also act as **release candidate** installers.
+The weekly snapshots of the nightly qgis-qt6-dev package of OSGeo4W are for users that cannot use OSGeo4W (see below) for some reason or just prefer standalone installers. In the feature freeze phase, these also act as **release candidate** installers.
 
 ## Online (OSGeo4W) installer
 
@@ -58,13 +58,20 @@ Alternatively, instead of doing the _Express_ install, you can use the _Advanced
 |Release|Version|Package|Description|
 |---|---|---|---|
 |Latest Release|{{< param "release" >}} {{< param "codename" >}} {{< param "releasenote" >}}|qgis|Release|
+|||qgis-qt6 |Release (Qt6)[[2]](#id2)|
 |||qgis-rel-dev [[1]](#id1)|Nightly build of the upcoming point release|
+|||qgis-qt6-rel-dev [[1]](#id1)|Nightly build of the upcoming point release (Qt6)[[2]](#id2)|
 |Long Term Release|{{< param "ltrrelease" >}} {{< param "ltrcodename" >}} {{< param "ltrnote" >}}|qgis-ltr|Release|
-|||qgis-ltr-dev [[1]](#id1)|Nightly build of the upcoming long term point release|
-|Development|{{< param "devversion" >}} master|qgis-dev [[1]](#id1)|Nightly build of the development version|
+|||qgis-qt6-ltr|Release (Qt6)[[2]](#id2)|
+|||qgis-ltr-dev [[1]](#id1)|Nightly build of the upcoming long term point release (Qt5)|
+|||qgis-qt6-ltr-dev [[1]](#id1)|Nightly build of the upcoming long term point release (Qt6)[[2]](#id2)|
+|Development|{{< param "devversion" >}} master|qgis-qt6-dev [[1]](#id1)|Nightly build of the development version|
+|||qgis-dev [[1]](#id1)|Nightly build of the development version (Qt5) [[2]](#id2)|
 
 {{< footnote "1" >}} Nightlies are debug builds (including debugging output that can be used by developers to better understand issues with the build).
 
+{{< footnote "2" >}} 3.99 will become 4.0 and mark the switch to Qt6.  Earlier versions of QGIS are experimental with Qt6. Starting with 3.99 only Qt6 is supported and Qt5 deprecated.
+
 The packages listed in the above table only install the necessary dependencies needed to run QGIS. Corresponding to those packages there are also meta packages with the suffix `-full-free` and `-full`. The `-full-free` contains additional optional dependencies that some popular (not included in the default QGIS install) plugins use.  The `-full` includes everything from `-full-free` and also adds proprietary extensions like Oracle drivers, ECW and MrSID.
 
 The Express installs reference the corresponding `-full` variant and the standalone installers are also made from these OSGeo4W package sets.

themes/hugo-bulma-blocks-theme/layouts/partials/download-windows-buttons.html

@@ -6,7 +6,11 @@
   <p class="is-6 mb-2">
     <strong>Online (OSGeo4W) installer</strong>
   </p>
-  <p class="is-size-7 mb-3">Best way to keep QGIS up to date and manage multiple versions</p>
+  <p class="is-size-7 mb-3">Best way to keep QGIS up to date and manage multiple versions.
+    <a class="has-text-dark" href="{{ absURL "resources/installation-guide#online-osgeo4w-installer" }}">
+        Learn more.
+    </a>
+  </p>
   <a class="button mr-0 is-primary2 is-fullwidth" 
       href="https://download.osgeo.org/osgeo4w/v2/osgeo4w-setup.exe"
       onclick="thanks(this)"