update readme with env var config options

README.md

@@ -14,14 +14,42 @@ message publishing and replication. Indexing of database messages will be
 offloaded to client applications (ie. piping feeds from solar into a SQLite
 database).
 
+## Quick Start
+
+Clone the source and build the binary (see [RPi build instructions](https://mycelial.technology/computers/rust-compilation.html) if required):
+
+```
+git clone [email protected]:mycognosist/solar.git
+cd solar
+cargo build --release
+```
+
+Add peer(s) to `replication.toml` (public key(s) of feeds you wish to replicate):
+
+```
+vim ~/.local/share/solar/replication.toml
+
+peers = ["@...=.ed25519"]
+```
+
+Run solar with LAN discovery enabled:
+
+```
+./target/release/solar --lan true
+```
+
+_Note: a new public-private keypair will be generated and saved to
+`~/.local/share/solar/secret.toml` (or in the equivalent directory on your
+operating system)._
+
 ## CLI
 
 Solar can be configured and launched using the CLI interface.
 
 `solar --help`
 
 ```shell
-🌞 Solar 0.3.1-6266b38
+🌞 Solar 0.3.1-1dad14c
 Sunbathing scuttlecrabs in kuskaland
 
 USAGE:
@@ -42,33 +70,21 @@ USAGE:
             --resync <resync>          Resync the local database by requesting the local feed from peers
 ```
 
-## Quick Start
-
-Clone the source and build the binary (see [RPi build instructions](https://mycelial.technology/computers/rust-compilation.html) if required):
-
-```
-git clone [email protected]:mycognosist/solar.git
-cd solar
-cargo build --release
-```
+## Environment Variables
 
-Add peer(s) to `replication.toml` (public key(s) of feeds you wish to replicate):
+Additional configuration parameters can be supplied via environment variables.
 
 ```
-vim ~/.local/share/solar/replication.toml
-
-peers = ["@...=.ed25519"]
+RUST_LOG
+SLED_CACHE_CAPACITY
+SOLAR_JSONRPC_IP
+SOLAR_JSONRPC_PORT
+SOLAR_NETWORK_KEY
 ```
 
-Run solar with LAN discovery enabled:
-
-```
-./target/release/solar --lan true
-```
+For example, run `solar` with a log-level of `debug` and an alternative network key:
 
-_Note: a new public-private keypair will be generated and saved to
-`~/.local/share/solar/secret.toml` (or in the equivalent directory on your
-operating system)._
+`RUST_LOG=solar=debug SOLAR_NETWORK_KEY=3c42fff79381c451fcafd73cec3c9f897bb2232949dcdd35936d64d67c47a374 solar`
 
 ## Core Features