README.md to include the named dirs description.

README.md

@@ -1077,6 +1077,25 @@ zi as'null' lucid sbin wait'1' for \
 
 Target directory for installed files is `$ZPFX` (`~/.local/share/zinit/polaris` by default).
 
+# Named directories for frequently used paths
+
+Named directories are shorthands in the form of `~NAMED_DIR`
+(upper case not required). Zinit provides a set of such
+names for its frequently used paths:
+
+- *~ZIDIR* → `$ZINIT[HOME_DIR]` – the home directory for others, like `plugins`, `snippets`, etc.
+- *~ZIPLUGS* → `$ZINIT[PLUGINS_DIR]` – the `plugins` dir,
+- *~ZISNIPS* → `$ZINIT[SNIPPETS_DIR]` – the `snippets` dir,
+- *~ZICOMPS* → `$ZINIT[COMPLETIONS_DIR]` – the `completions` dir, where all
+completion functions reside`
+- *~ZISERV* → `$ZINIT[SERVICES_DIR]` – the `services` work dir for all loaded
+services,
+- *~ZICACHE* → `$ZSH_CACHE_DIR` – the cache dir, usually `~/.cache/zinit`,
+- *~ZIBIN* → `$ZINIT[BIN_DIR]` – the directory with Zinit's binary scripts,
+- *~ZPFX* → the standard prefix for all `configure` and `make` commands, usually
+            `~ZIDIR/polaris`.
+
+
 ## Changelog<a name="changelog"></a>
 
 Link to the [CHANGELOG](doc/CHANGELOG.md).