Add usage examples to README.md

README.md

@@ -13,3 +13,40 @@ The `nextfile` library actually contains two exported modules, `nextfile` and `p
 - If the previous filename ends in a letter, then the next file will bump it to the next letter. For example, if the previous file were "200a.png", the next file would be "200b.png".
 
 By default, `nextfile` will give the next file the same file extension as the previous file; there is a second optional parameter for specifying the file extension.
+
+## Examples
+
+### Create Test Files
+```sh
+user@box:~$ cd $(mktemp -d)
+user@box:/tmp/tmp.g9nf7G4U1C $ touch {1,2,3}.txt
+```
+
+### Use prevfile
+```lua
+local prevfile = require("prevfile")
+local pfile = prevfile.prevfile("/tmp/tmp.g9nf7G4U1C")
+print(pfile) -- 3.txt
+```
+
+### Use nextfile
+```lua
+local nextfile = require("nextfile")
+local nfile = nextfile.nextfile("/tmp/tmp.g9nf7G4U1C")
+print(nfile) -- 4.txt
+
+-- Specify an alternate file extension
+nfile = nextfile.nextfile("/tmp/tmp.g9nf7G4U1C", "png")
+print(nfile) -- 4.png
+```
+
+### Create Alphabetical Test File
+```sh
+user@box:/tmp/tmp.g9nf7G4U1C $ touch 4a.txt
+```
+
+```lua
+local nextfile = require("nextfile")
+local nfile = nextfile.nextfile("/tmp/tmp.g9nf7G4U1C")
+print(nfile) -- 4b.txt
+```