add docu (as readme)

README.md

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+# Object Store
+
+Objects are are pieces of information split into Metadata and Data.
+They can be stored seperated or together.
+They can be used as a Transport protocol/logic too.
+
+[see wikipedia](https://en.wikipedia.org/wiki/Object_store)
+
+# Store types
+
+### Filesystem Store
+
+Fragment files are stored with the first 2 hex chars as sub folders:
+eg:
+`objects/` (object store root)
+  - `5f/` (first 2hex subfolder)
+    - `4fffffff` (the fragment file without the first 2 hexchars)
+
+Metadata and data stored in seperate files.
+Metadata files have the `.meta` suffix. They also have a filetype specific suffix, like `.json`, `.msgpack` etc.
+(single file objects are planned but no ETA)
+
+### Memory Store
+
+Just keeps the Fragments in memory.
+
+# File formats
+
+Files can be compressed and encrypted. Since compression needs the data's structure to work properly, it is applied before it is encrypted.
+
+### Text Json
+
+Text json only makes sense for metadata if it's neither compressed nor encrypted. (otherwise its binary on disk anyway, so why waste bytes).
+Since the content of data is not looked at, nothing stops you from using text json and ecrypt it, but atleast basic compression is advised.
+
+A Metadata json object can have arbitrary keys, some are predefined:
+- `FragComp::DataEncryptionType` (uint) Encryption type of the data, if any
+- `FragComp::DataCompressionType` (uint) Compression type of the data, if any
+
+### Binary msgpack
+
+msgpack array:
+
+- `[0]`: file magic string `SOLMET` (6 bytes)
+- `[1]`: uint8 encryption type (`0x00` is none)
+- `[2]`: uint8 compression type (`0x00` is none, `0x01` is zstd)
+- `[3]`: binary metadata (optionally compressed and encrypted)
+
+note that the encryption and compression are for the metadata only.
+The metadata itself contains encryption and compression info about the data.
+
+### Split Data
+
+All the metadata is in the metadata file. (like encryption and compression)
+This is mostly to allow direct storage for files in the Fragment store without excessive duplication.
+Keep in mind to not use the actual file name as the data/meta file name.
+
+## Compression types
+
+- `0x00` none
+- `0x01` zstd (without dict)
+
+zstd with hardcoded dictionaries will come later.