Filled out README.md with cursory content.

README.md

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 # static-file-server
 Tiny, simple static file server using environment variables for configuration
+
+Available on Docker Hub at https://hub.docker.com/r/halverneus/static-file-server/
+
+Environment variables with defaults:
+```
+HOST=
+PORT=8080
+FOLDER=/web
+```
+
+### Without Docker
+```
+PORT=8888 FOLDER=. ./serve
+```
+Files can then be accessed by going to http://localhost:8888/my/file.txt
+
+### With Docker
+docker run -d -v /my/folder:/web -e PORT=9090 -p 9090:9090 halverneus/static-file-server:latest
+
+This will serve the folder "/my/folder" over http://localhost:9090/my/file.txt