doc: update README.md

Author: OUDON

README.md

@@ -5,17 +5,17 @@
 This is an rMQR Code image generator implemented in Python. This is implemented based on [ISO/IEC 23941:2022](https://www.iso.org/standard/77404.html).
 
 
-## Important Notice
+## 📌 Important Notice
 Please verify an image generated by this software whether it can decode correctly before use.
 
 
-## Installation
+## 🚀 Installation
 ```
 pip install rmqrcode
 ```
 
 
-## Basic Usage
+## 📕 Basic Usage
 ### Generate rMQR Code
 ```py
 from rmqrcode import rMQR
@@ -29,11 +29,11 @@ qr = rMQR.fit(
 )
 ```
 
-The `ecc` parameter is an enum value of rmqrcode.ErrorCorrectionLevel to select error correction level. The following values are available:
+The `ecc` parameter is an enum value of `rmqrcode.ErrorCorrectionLevel` to select error correction level. The following values are available:
 - **`ErrorCorrectionLevel.M`**: Approx. 15% Recovery Capacity.
 - **`ErrorCorrectionLevel.H`**: Approx. 30% Recovery Capacity.
 
-The `fit_strategy` parameter is enum value of rmqrcode.FitStrategy to specify how to determine size of rMQR Code. The following values are available:
+The `fit_strategy` parameter is enum value of `rmqrcode.FitStrategy` to specify how to determine size of rMQR Code. The following values are available:
 - **`FitStrategy.MINIMIZE_WIDTH`**: Try to minimize width.
 - **`FitStrategy.MINIMIZE_HEIGHT`**: Try to minimize height.
 - **`FitStrategy.BALANCED`**: Try to keep balance of width and height.
@@ -51,7 +51,7 @@ image.save("my_qr.png")
 ```
 
 
-## Advanced Usage
+## 📚 Advanced Usage
 ### Select rMQR Code size manually
 To select rMQR Code size manually, use `rMQR()` constructor.
 ```py
@@ -62,7 +62,7 @@ qr.make("https://oudon.xyz")
 `R11x139` means 11 rows and 139 columns. The following table shows available combinations.
 
 | |27|43|59|77|99|139|
-|-|-|-|-|-|-|-|
+|-|:-:|:-:|:-:|:-:|:-:|:-:|
 |R7|❌|✅|✅|✅|✅|✅|
 |R9|❌|✅|✅|✅|✅|✅|
 |R11|✅|✅|✅|✅|✅|✅|
@@ -71,6 +71,18 @@ qr.make("https://oudon.xyz")
 |R17|❌|✅|✅|✅|✅|✅|
 
 
+## 🛠️ Under the Hood
+### Encoding modes
+
+The rMQR Code has the four encoding modes Numeric, Alphanumeric, Byte and Kanji to convert data efficiently. However, this package supoprts only Byte mode currently.
+
+|Mode|Supported?|
+|-|:-:|
+|Numeric| |
+|Alphanumeric||
+|Byte|✅|
+|Kanji||
+
 ----
 The word "QR Code" is registered trademark of DENSO WAVE Incorporated.<br>
 http://www.denso-wave.com/qrcode/faqpatent-e.html