tweak doc branch graph (#567)

* tweak doc branch graph

* Fix link anchor

---------

Co-authored-by: Daniil Gusev <daniil@quix.io>

Author: tim-quix

docs/branching.md

@@ -12,24 +12,24 @@ Before branching, only this was possible:
 
 ```
 sdf
-└── A
-    └── B
-        └── C
-            └── D
+└── apply()
+    └── apply()
+        └── apply()
+            └── apply()
 ```
 
 But with branching, you could do something like:
 
 ```
 sdf
-└── A
-    └── B
-        ├── C
-        │   └── D
-        └── E
-            ├── F
-            ├── G
-            └── H
+└── apply()
+    └── apply()
+        ├── apply()
+        │   └── apply()
+        └── filter() - (does following operations only to this filtered subset)
+            ├── apply()
+            ├── apply()
+            └── apply()
 ```
 
 ## Branching Use Cases

docs/connectors/sources/custom-sources.md

@@ -46,7 +46,7 @@ This is the base class for all sources. It handles configuring the source and re
 * `stop`: This method is called, in the subporcess, when the application is shutting down.
 * `default_topic`: This method is called, in the main process, when a topic is not provided with the source.
 
-For more information, see [`quixstreams.sources.base.BaseSource`](../../api-reference/sources.md#BaseSource) docstrings.
+For more information, see [`quixstreams.sources.base.BaseSource`](../../api-reference/sources.md#basesource) docstrings.
 
 ## Custom Sources and Jupyter Notebook