add deprecation warnings throughout docs

docs/customize/SQLite.md

@@ -12,11 +12,16 @@ To use a SQLite database, you need to install:
 
 * SQLite (>= 3.30)
 * Spatialite (> 5.0.0)
+* aiosqlite
 
 On Ubuntu/Debian, you can run:
 
     sudo apt install sqlite3 libsqlite3-mod-spatialite libspatialite7
 
+Install the aiosqlite Python package in your virtual environment:
+
+    /srv/nominatim-venv/bin/pip install aiosqlite
+
 ## Creating a new SQLite database
 
 Nominatim cannot import directly into SQLite database. Instead you have to

docs/customize/Tokenizers.md

@@ -17,6 +17,11 @@ they can be configured.
 
 ## Legacy tokenizer
 
+!!! danger
+    The Legacy tokenizer is deprecated and will be removed in Nominatim 5.0.
+    If you still use a database with the legacy tokenizer, you must reimport
+    it using the ICU tokenizer below.
+
 The legacy tokenizer implements the analysis algorithms of older Nominatim
 versions. It uses a special Postgresql module to normalize names and queries.
 This tokenizer is automatically installed and used when upgrading an older