update toc

Signed-off-by: Wenqi Li <[email protected]>

Author: wyli

docs/source/config_syntax.md

@@ -8,6 +8,9 @@ The main benefits are threefold:
 - it describes workflow at a relatively high level and allows for different low-level implementations.
 - learning paradigms at a higher level such as federated learning and AutoML can be decoupled from the component details.
 
+- [A basic example](#a-basic-example)
+- [Syntax examples explained](#syntax-examples-explained)
+
 ## A basic example
 
 Components as part of a workflow can be specified using `JSON` or `YAML` syntax, for example, a network architecture
@@ -62,10 +65,14 @@ or additionally, tune the input parameters then instantiate the component:
 BasicUNet features: (32, 32, 32, 64, 64, 64).
 ```
 
+For more details on the `ConfigParser` API, please see https://docs.monai.io/en/latest/bundle.html#config-parser.
+
 ## Syntax examples explained
 
 A few characters and keywords are interpreted beyond the plain texts, here are examples of the syntax:
 
+### `@` to interpolate with Python objects
+
 ```json
 "@preprocessing#transforms#keys"
 ```
@@ -79,6 +86,8 @@ where `#` indicates a sub-structure of this configuration file.
 
 _Description:_ `1` is interpreted as an integer, which is used to index the `preprocessing` sub-structure.
 
+### `$` to evaluate as Python expressions
+
 ```json
 "$print(42)"
 ```
@@ -91,6 +100,8 @@ _Description:_ `$` is a special character to indicate evaluating `print(42)` at
 
 _Description:_ Create a list at runtime using the values in `datalist` as input.
 
+### `_target_` to instantiate a Python object
+
 ```json
 {
   "demo_name":{