docs: change default max_feature_count documentation to null (#1706)

Document `null` as less confusing than `~`

docs/src/config-file.md

@@ -69,8 +69,7 @@ postgres:
   # If the source table has more features than set here, they will not be included in the tile and the result will look "cut off"/incomplete.
   # This feature allows to put a maximum latency bound on tiles with extreme amount of detail at the cost of not returning all data.
   # It is sensible to set this limit if you have user generated/untrusted geodata, e.g. a lot of data points at [Null Island](https://en.wikipedia.org/wiki/Null_Island).
-  # `null` (the default): Unlimited
-  max_feature_count: 100_000
+  max_feature_count: null # either a positive integer, or null=unlimited (default)
 
   # Control the automatic generation of bounds for spatial tables [default: quick]
   # 'calc' - compute table geometry bounds on startup.