Update readme for adding PostGIS example and migrating slack community

README.md

@@ -13,7 +13,7 @@ Library for handling diffs for geospatial data. Works with GeoPackage files and
 
 Geodiff library is used by [Mergin Maps](https://merginmaps.com/) - a platform for easy sharing of spatial data.
 
-<div><img align="left" width="45" height="45" src="https://raw.githubusercontent.com/MerginMaps/docs/main/src/public/slack.svg"><a href="https://merginmaps.com/community/join">Join our community chat</a><br/>and ask questions!</div>
+<a href="https://community.merginmaps.com">Join our community</a> and ask questions!
 
 ## Use cases for geodiff
 
@@ -49,6 +49,8 @@ The library nowadays comes with support for two drivers:
 
 ## Using command line interface
 
+### GeoPackage
+
 To get changes between two GeoPackage files and write them to `a-to-b.diff` (a binary diff file):
 ```bash
 geodiff diff data-a.gpkg data-b.gpkg a-to-b.diff
@@ -70,6 +72,23 @@ geodiff invert a-to-b.diff b-to-a.diff
 geodiff apply data-a.gpkg b-to-a.diff
 ```
 
+### PostGIS
+
+The same commands work with PostGIS databases. Instead of file paths, pass **schema names** and use `--driver postgres` with a [libpq connection string](https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-CONNSTRING):
+```bash
+geodiff diff --driver postgres "host=localhost dbname=mydb user=myuser password=mypass" schema_a schema_b a-to-b.diff
+```
+
+```bash
+geodiff diff --json --driver postgres "host=localhost dbname=mydb user=myuser password=mypass" schema_a schema_b
+```
+
+```bash
+geodiff apply --driver postgres "host=localhost dbname=mydb user=myuser password=mypass" schema_a a-to-b.diff
+```
+
+Both schemas must be in the same database and have identical table structure. You can check which drivers are available with `geodiff drivers`.
+
 The `geodiff` tool supports other various commands, use `geodiff help` for the full list.
 
 ## Using Python module
@@ -82,6 +101,8 @@ pip3 install pygeodiff
 If you get error `ModuleNotFoundError: No module named 'skbuild'` try to update pip with command
 `python -m pip install --upgrade pip`
 
+### GeoPackage
+
 Sample usage of the Python module:
 
 ```python
@@ -99,6 +120,37 @@ geodiff.apply_changeset('data-a.gpkg', 'a-to-b.diff')
 geodiff.list_changes('a-to-b.diff', 'a-to-b.json')
 ```
 
+### PostGIS
+
+To perform the same actions against a PostGIS database, use the `_ex` methods with a driver name and connection string. The `base` and `modified` arguments are schema names:
+
+```python
+import pygeodiff
+
+geodiff = pygeodiff.GeoDiff()
+conninfo = "host=localhost dbname=mydb user=myuser password=mypass"
+
+# create a diff between two PostGIS schemas
+geodiff.create_changeset_ex(
+    driver="postgres",
+    driver_info=conninfo,
+    base="schema_a",
+    modified="schema_b",
+    changeset="a-to-b.diff"
+)
+
+# apply changes from a-to-b.diff to a PostGIS schema
+geodiff.apply_changeset_ex(
+    driver="postgres",
+    driver_info=conninfo,
+    base="schema_a",
+    changeset="a-to-b.diff"
+)
+
+# export changes from the binary diff format to JSON
+geodiff.list_changes('a-to-b.diff', 'a-to-b.json')
+```
+
 If there are any problems, calls will raise `pygeodiff.GeoDiffLibError` exception.
 
 If you have Mergin plugin for QGIS installed, you can also use pygeodiff from QGIS' Python Console by starting with