Add version

README.md

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-# HEIC2JPG
+# HEIC2JPG
+
+## Usage
+
+To convert a single file:
+
+`heic2jpg myfile.heic`
+
+To convert all files in a folder:
+
+`heic2jpg -dir ./MyPhotos -r`
+
+You can create new files in another folder with the `-o` argument
+
+Other arguments are available on `-h`
+
+## Build
+
+The tool contains C code, so you need to activate cgo to compile it.
+
+`go build`
+
+I compile with the following command (not sure if it speeds up conversion, but it makes the binary lighter):
+
+On Linux:
+```bash
+GOAMD64='v3' go build -a -v -ldflags="-s -w" -buildvcs=false
+```
+
+On Windows (PowerShell):
+```ps
+$env:GOAMD64 = 'v3'; go build -a -v -ldflags="-s -w" -buildvcs=false
+```