add configuration section to README explaining common gotchas

README.md

@@ -16,13 +16,15 @@ This is configurable in your [`.env`](.env.example) file.
 See [docker-compose.yaml](./docker-compose.yaml).
 
 ### Usage
-- Install Docker with Docker compose
-- Clone repository
-- Run `cp .env.example .env` and configure it (see [example](#example-env))
-- Run `docker-compose up`
-- Visit your domain
+
+1. Install Docker with Docker Compose https://get.docker.com/
+2. Clone this repository `git clone https://github.com/timvisee/send-docker-compose`
+3. Run `cp .env.example .env` and configure it (see [example](#example-env))
+4. Run `docker-compose up`
+5. Visit your domain
 
 ### Example .env
+
 ```bash
 # Docker image to use for Send
 # - Latest Send version by @timvisee: registry.gitlab.com/timvisee/send:latest
@@ -41,3 +43,39 @@ LETSENCRYPT_HOST=
 # Optional: for LetsEncrypt SSL, your email address
 LETSENCRYPT_EMAIL=mail@example.org
 ```
+
+### Configuration
+
+All the config options and their defaults can be found here: https://github.com/timvisee/send/blob/master/server/config.js.
+
+Config options expecting array values (e.g. `EXPIRE_TIMES_SECONDS`, `DOWNLOAD_COUNTS`) are parsed as CSV, and the first entry is the default.
+
+Other options should be set as unquoted strings, integers, booleans, etc., for example:
+```yaml
+...
+services:
+  ...
+  send:
+    ...
+    environment:
+      ...
+
+      # strings numbers, bools, etc. shoul all be set as bare unquoted values
+      - BASE_URL=https://send.example.com
+      - DHPARAM_GENERATION=false
+      - MAX_DOWNLOADS=250000
+
+      # use values set in the .env using ${VARNAME} bash syntax
+      - VIRTUAL_HOST=${HOST}
+      
+      # time values are all in seconds, e.g. 365d * 60*60*24 = 31,536,000 seconds
+      - MAX_EXPIRE_SECONDS=31536000
+      - DEFAULT_EXPIRE_SECONDS=86400
+
+      # array configs are set as CSV (first entry is the default for the UI dropdown)
+      - EXPIRE_TIMES_SECONDS=86400,3600,86400,604800,2592000,31536000,157680000
+      - DOWNLOAD_COUNTS=10,1,2,5,10,15,25,50,100,1000,10000,100000,250000
+      
+      # size values are are in bytes, e.g. 10GB * 1024*1024*1024 = 10,747,904,000 bytes
+      - MAX_FILE_SIZE=10747904000
+```