docs: fix typos and wording for the persistent-nodemap feature

Differential Revision: https://phab.mercurial-scm.org/D11810

mercurial/helptext/config.txt

@@ -923,27 +923,29 b' https://www.mercurial-scm.org/wiki/Missi'
 
 ``use-persistent-nodemap``
     Enable or disable the "persistent-nodemap" feature which improves
-    performance if the rust extensions are available.
-
-    The "persistence-nodemap" persist the "node -> rev" on disk removing the
+    performance if the Rust extensions are available.
+
+    The "persistent-nodemap" persist the "node -> rev" on disk removing the
     need to dynamically build that mapping for each Mercurial invocation. This
-    significantly reduce the startup cost of various local and server-side
-    operation for larger repository.
-
-    The performance improving version of this feature is currently only
-    implemented in Rust, so people not using a version of Mercurial compiled
-    with the Rust part  might actually suffer some slowdown. For this reason,
-    Such version will by default refuse to access such repositories. That
-    behavior can be controlled by configuration. Check
+    significantly reduces the startup cost of various local and server-side
+    operation for larger repositories.
+
+    The performance-improving version of this feature is currently only
+    implemented in Rust (see :hg:`help rust`), so people not using a version of
+    Mercurial compiled with the Rust parts might actually suffer some slowdown.
+    For this reason, such versions will by default refuse to access repositories
+    with "persistent-nodemap".
+
+    This behavior can be adjusted via configuration: check
     :hg:`help config.storage.revlog.persistent-nodemap.slow-path` for details.
 
-    Repository with this on-disk format require Mercurial version 5.4 or above.
-
-    By default this format variant is disabled if fast implementation is not
-    available and enabled by default if the fast implementation is available.
-
-    To accomodate install of Mercurial without the fast implementation you can
-    downgrade your repository. To do so run the following command:
+    Repositories with this on-disk format require Mercurial 5.4 or above.
+
+    By default this format variant is disabled if the fast implementation is not
+    available, and enabled by default if the fast implementation is available.
+
+    To accomodate installations of Mercurial without the fast implementation,
+    you can downgrade your repository. To do so run the following command:
 
     $ hg debugupgraderepo \
           --run \