Fix wording, formatting and link in offline upgrade/downgrade

Changes:
* reformat the last step of the offline upgrade section so that
  instructions and their descriptions are more clear
* update `reindex` command link to version `3.10.0`
* replace `v3.7/v3.8` with `v3.9` in downgrade section
* rephrase the step 3 so that it doesn't refer to `changes` as all
  indices will be affected
* reformat downgrade section so that code snippet is part of step 3
  and step 4 correctly numbered

Change-Id: I8376197e56ec5b6076c8d0bf9cbfa913864b54c2
diff --git a/pages/site/releases/3.10.md b/pages/site/releases/3.10.md
index 2f0ef25..0698b6d 100644
--- a/pages/site/releases/3.10.md
+++ b/pages/site/releases/3.10.md
@@ -207,26 +207,28 @@
   (see Online index schema upgrade from 3.9 above). If you still want to you
   will need to run reindex:
 
-  `java -jar gerrit.war reindex -d site_path` If you are upgrading from a 3.8 or
-  an earlier version, you must run a reindex of all indexes:
+  `java -jar gerrit.war reindex -d site_path`
 
-  `java -jar gerrit.war reindex -d site_path` See the
-  [reindex](https://gerrit-documentation.storage.googleapis.com/Documentation/3.9.0/pgm-reindex.html)
+  If you are upgrading from a 3.8 or an earlier version, you must run a reindex
+  of all indexes:
+
+  `java -jar gerrit.war reindex -d site_path`
+
+  See the
+  [reindex](https://gerrit-documentation.storage.googleapis.com/Documentation/3.10.0/pgm-reindex.html)
   command for other options.
 
 ### Downgrade
- Downgrade to any Gerrit v3.9 release is possible, but requires the following
+Downgrade to Gerrit v3.9 release is possible, but requires the following
 manual steps:
 
 1. Shutdown all migrated Gerrit servers
-2. Update the gerrit.war and plugins to the previous v3.7/v3.8 version
-3. Run offline change reindexing using the previous gerrit.war version
-
-```sh
-  java -jar gerrit.war init -d site_path --batch
-  java -jar gerrit.war reindex -d site_path
-```
-
+2. Update the gerrit.war and plugins to the previous v3.9 version
+3. Run offline reindexing using the previous gerrit.war version
+  ```sh
+    java -jar gerrit.war init -d site_path --batch
+    java -jar gerrit.war reindex -d site_path
+  ```
 4. Startup Gerrit server
 
 ### Native packaging