Update README docs

README.md

@@ -1,6 +1,68 @@
 # c-polygonid
 
-C wrapper for polygonid libraries.
+This is a wrapper library for several PolygonID Go libraries, designed for use
+with C/C++ languages. It can also be used in mobile development or other
+infrastructures facing challenges with Go integration.
+
+An overview of the major functions looks like this:
+```
+GoUint8 PLGNAtomicQuerySigV2Inputs(char** jsonResponse, char* jsonRequest, char* cfg, PLGNStatus** status);
+```
+
+`GoUint8` is a type alias for `signed char`, which essentially represents a Go
+bool. It can be `0` or `1`. Generally, the function returns `1` in the event of
+a successful operation and `0` in the event of failure.
+
+If the `status` pointer is not NULL, a new PLGNStatus object will be allocated,
+containing details about errors. This object should be freed with the
+`PLGNStatusFree` function to avoid a memory leak.
+
+`jsonRequest` and `jsonResponse` are plain JSON objects. Their contents depend
+on the specific function and should be documented in the
+[polygonid.go](cmd/polygonid/polygonid.go) file. The examples of requests to
+different functions can be found in [testdata](testdata) directory.
+
+## Configuration
+
+The configuration object is a JSON document with the following structure:
+```json5
+{
+  "ipfsNodeUrl": "http://localhost:5001", // IPFS Node URL
+  "chainConfigs": {
+    "1": { // Chain ID as decimal
+      "rpcUrl": "http://localhost:8545", // RPC URL
+      "stateContractAddr": "0xEA9aF2088B4a9770fC32A12fD42E61BDD317E655" // State contract address
+    },
+    "0x10": { // Chain ID in hexadecimal format
+      "rpcUrl": "http://localhost:8545",
+      "stateContractAddr": "0xEA9aF2088B4a9770fC32A12fD42E61BDD317E655"
+    }
+  }
+}
+```
+
+This object should be passed on each call to the library.
+It is not memorized or cached.
+
+## Errors
+
+In case of an error, the function returns `0`, and if the pointer to the
+`PLGNStatus` struct is not NULL, a struct object will be allocated and filled
+with the following structure:
+
+```C
+typedef struct _PLGNStatus
+{
+	PLGNStatusCode status;
+	char *error_msg;
+} PLGNStatus;
+```
+
+Here, `PLGNStatusCode` is the status enum that can be seen in the .h file
+included in the distribution of this library, and `error_msg` is a string
+containing a detailed, human-readable error.
+
+This object should be freed with `PLGNStatusFree` function.
 
 ## Build on macos M1
 
@@ -32,4 +94,4 @@ clang -L../ios -lpolygonid-darwin-arm64 \
         -framework CoreServices \
         `pkg-config --libs --cflags libcjson` \
         json_functions_tests.c && ./a.out
-```
+```