docs: extend docs with the different node configuration mechanisms

docs/operators/how-to/configure.md

@@ -1,12 +1,135 @@
 # Configure a nwaku node
 
 Nwaku can be configured to serve the adaptive needs of different operators.
-This page serves as an index of tutorials explaining how to configure your nwaku node for different use cases.
+
+> :bulb: **Tip:** The recommended configuration method is through environment variables.
+
+## Node configuration methods
+
+One node can be configured using a combination of the following methods:
+
+1. Command line options and flags
+2. Environment variables
+3. Configuration file (currently, only TOML format is supported)
+4. Default value
+
+Note the precedence order, each configuration mechanism overrides the configuration set by one below (e.g., _command line options_ override the configuration set by the _environment variables_ and by the _configuration file_).
+
+### Command line options/flags
+
+The main mechanism to configure the node is via command line options. Any configuration option provided via the command line will override any other configuration mechanism.
+
+> :warning: nwaku is under heavy development. It is likely that configuration will change from one version to another.
+>
+> If after an upgrade, the node refuses to start, check if any of the command line configuration options provided to the node have been changed or removed.
+> 
+> To overcome this issue, we recommend to configure the node via environment variables.
+
+The configuration options should be provided after the binary name as follows:
+
+```shell
+wakunode2 --tcp-port=65000
+```
+
+In the case of using docker to run you node you should provide the commandline options after the image name as follows:
+
+```shell
+docker run statusteam/nim-waku --tcp-port=65000
+```
+
+Run `wakunode2 --help` to get a comprehensive list of configuration options (and its default values):
+
+```shell
+$ wakunode2 --help
+Usage: 
+
+wakunode2 [OPTIONS]...
+
+The following options are available:
+
+ --config-file             Loads configuration from a TOML file (cmd-line parameters take precedence).
+ --log-level               Sets the log level. [=LogLevel.INFO].
+ --version                 prints the version [=false].
+
+<...>
+```
+
+Check the configuration tutorials for specific configuration use cases.
+
+### Environment variables
+
+The node can also be configured via environment variables. 
+
+> :information_source: Support for configuring the node via environment variables was added in v0.13.0
+
+The environment variable name should be prefixed by the app's name, in this case `WAKUNODE2_` followed by the commandline option in [screaming snake case](https://en.wiktionary.org/wiki/screaming_snake_case). 
+
+For example, to set the `--tcp-port` configuration we should call `wakunode2` binary as follows:
+
+```shell
+WAKUNODE2_TCP_PORT=65000 wakunode2
+```
+
+In the case of using docker to run you node you should start the node using the `-e` command options:
+
+```shell
+docker run -e "WAKUNODE2_TCP_PORT=65000" statusteam/nim-waku
+```
+
+This is the second configuration method in order of precedence. Any command line configuration option will override the configuration
+provided via environment variables.
+
+### Configuration file
+
+The third configuration mechanism in order of precedence is the configuration via a TOML file. The previous mechanims take precedence over this mechanism as explained above.
+
+The configuration file follows the [TOML](https://toml.io/en/) format:
+
+```toml
+log-level = "DEBUG"
+tcp-port = 65000
+```
+
+The path to the TOML file can be specified usin one of the previous configuration mechanisms:
+
+* By passing the `--config-file` command line option:
+  ```shell
+  wakunode2 --config-file=<path-to-toml-config-file>
+  ```
+* By passing the path via environment variables:
+  ```shell
+  WAKUNODE2_CONFIG_FILE=<path-to-toml-config-file> wakunode2
+  ```
+
+### Configuration default values
+
+As usual, if no configuration option is specified by any of the previous mechanisms, the default configuration will be used.
+
+The default configuration value is listed in the `wakunode2 --help` output:
+
+```shell
+$ wakunode2 --help
+Usage: 
+
+wakunode2 [OPTIONS]...
+
+The following options are available:
+
+ --config-file             Loads configuration from a TOML file (cmd-line parameters take precedence).
+ --log-level               Sets the log level. [=LogLevel.INFO].
+ --version                 prints the version [=false].--tcp-port                TCP listening port. [=60000].
+ --websocket-port          WebSocket listening port. [=8000].
+<...>
+```
+
+## Configuration use cases
+
+This an index of tutorials explaining how to configure your nwaku node for different use cases.
 
 1. [Connect to other peers](./connect.md)
 2. [Configure a domain name](./configure-domain.md)
 3. [Use DNS discovery to connect to existing nodes](./configure-dns-disc.md)
-4. [Configure store protocol](./configure-store.md)
+4. [Configure store protocol and message store](./configure-store.md)
 5. [Generate and configure a node key](./configure-key.md)
 6. [Configure websocket transport](./configure-websocket.md)
-7. [Run nwaku with rate limiting enabled](./run-with-rln.md)
+7. [Run nwaku with rate limiting enabled](./run-with-rln.md)