Added Readme.md with initial info.

Readme.md

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+# exif_rad
+
+A simple unix-style cross-platform Python 3 tool which can write certain tags to an image file.
+
+It can scan a couple of images, extract their Exif-tags, and compare the 'DateTimeOriginal' with other sources.
+
+By now it can parse a .his (CSV) file from a GeigerLog file export and calculate the radiation in µS/h using the factor in SIFACTOR.
+
+It then creates a 'UserComment' Exif tag with the actual measured radiation at the time the photo has been taken.
+
+## Dependencies
+Right now it depends on the following Python 3 libraries:
+
+  * PIL (core library)
+  * datetime (core library)
+  * Image (core library)
+  * math (core library)
+  * piexif
+  * gpxpy
+
+## Requirements
+  * GeigerCounter log file in csv format as it is being exported by the software GeigerLog. Such files look like this: `149654, 2020-02-27 05:12:42,    13.0,     0.0`
+  * A bunch of images (jpg, cr2, etc.) with its time of creation stored in 'DateTimeOriginal'
+  * A gpx track
+
+All sources are matched by their timestamp, so all sources have to be recorded during the same time.
+
+## Usage
+
+to-do
+
+## future possibilities
+
+In the future it should also be able to do the same with a gpx-file to extract geolocations and to write them into the appropiate Exif-fields.