📝 docs(_add): guide to generate gpg keys

docs/dev_guide/gpg_key.md

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-# Generate GPG Key
+# Generate GPG Key
+### 🔐 How to Generate a GPG Key on Snigdha OS
+
+GPG (GNU Privacy Guard) is a tool for secure communication and data encryption. It allows you to create and manage public and private keys, encrypt files, and sign documents. Here’s how you can generate a GPG key on Snigdha OS, step by step, with examples.
+
+---
+
+### 🛠️ Step 1: Install GPG
+
+Most Snigdha OS installations come with GPG pre-installed. If it’s not installed, use the following command to install it:
+
+```bash
+sudo pacman -S gnupg
+```
+
+To verify the installation, check the version:
+
+```bash
+gpg --version
+```
+
+---
+
+### 🛠️ Step 2: Create a New GPG Key Pair
+
+1. **Start the key generation process**:
+
+   Run the following command:
+
+   ```bash
+   gpg --full-generate-key
+   ```
+
+2. **Select the key type**:
+
+   You’ll see a prompt to choose the type of key. Options typically include:
+   - **(1) RSA and RSA (default)**
+   - (2) DSA and Elgamal
+   - (3) DSA (sign only)
+   - (4) RSA (sign only)
+
+   Press `1` and hit Enter to select the default **RSA and RSA** type.
+
+3. **Set the key length**:
+
+   You’ll be prompted to specify the key size. A common recommendation is **4096 bits** for strong encryption. Type `4096` and press Enter.
+
+4. **Set the expiration date**:
+
+   You can define how long the key should be valid. Options include:
+   - `0` for no expiration
+   - Specify a duration, e.g., `1y` for one year, `2y` for two years, or `1m` for one month.
+
+   For this example, type `0` (no expiration) and press Enter. When prompted, confirm your choice.
+
+5. **Enter your details**:
+
+   You’ll be asked for:
+   - **Your real name**: Enter your full name.
+   - **Your email address**: Enter a valid email address.
+   - **A comment (optional)**: Add a description or leave it blank.
+
+   Example:
+   ```
+   Real name: John Doe
+   Email address: johndoe@example.com
+   Comment: Snigdha OS User
+   ```
+
+   Review the details and confirm by typing `O` (for OK).
+
+6. **Set a passphrase**:
+
+   Choose a strong passphrase to protect your private key. This passphrase will be required whenever you use your private key for encryption or signing.
+
+---
+
+### 🛠️ Step 3: Verify the Generated Key
+
+Once the key is generated, you can list your keys with:
+
+```bash
+gpg --list-keys
+```
+
+Output:
+```
+/home/username/.gnupg/pubring.kbx
+---------------------------------
+pub   rsa4096 2023-12-05 [SC] [expires: 2025-12-05]
+      ABCD1234EFGH5678IJKL9012MNOP3456QRST7890
+uid           [ultimate] John Doe <johndoe@example.com>
+sub   rsa4096 2023-12-05 [E] [expires: 2025-12-05]
+```
+
+- **pub**: Your primary key (for signing and certification).  
+- **sub**: Subkey (for encryption).  
+- **[SC]**: Key capabilities: Sign and Certify.  
+- **[E]**: Encryption.  
+
+---
+
+### 🛠️ Step 4: Export Your Public Key
+
+To share your public key with others, export it:
+
+```bash
+gpg --armor --export johndoe@example.com > public_key.asc
+```
+
+This creates a file `public_key.asc` with your public key in ASCII format.
+
+To display the key in the terminal:
+
+```bash
+gpg --armor --export johndoe@example.com
+```
+
+---
+
+### 🛠️ Step 5: Test Encryption and Decryption
+
+1. **Encrypt a file**:
+
+   Create a sample file to encrypt:
+
+   ```bash
+   echo "Hello, this is a test message!" > message.txt
+   ```
+
+   Encrypt the file with your public key:
+
+   ```bash
+   gpg --output message.txt.gpg --encrypt --recipient johndoe@example.com message.txt
+   ```
+
+   This generates an encrypted file `message.txt.gpg`.
+
+2. **Decrypt the file**:
+
+   Decrypt the file using your private key:
+
+   ```bash
+   gpg --output decrypted_message.txt --decrypt message.txt.gpg
+   ```
+
+   Enter your passphrase when prompted. The decrypted content will be saved in `decrypted_message.txt`.
+
+---
+
+### 🛠️ Step 6: Back Up Your Keys
+
+Always back up your keys to prevent losing access:
+
+1. **Export your private key**:
+
+   ```bash
+   gpg --armor --export-secret-keys johndoe@example.com > private_key.asc
+   ```
+
+2. **Export your public key**:
+
+   ```bash
+   gpg --armor --export johndoe@example.com > public_key.asc
+   ```
+
+3. Store these files (`private_key.asc` and `public_key.asc`) in a safe place.
+
+---
+
+### 🚀 Final Tips
+
+- Keep your private key secure. Never share it.  
+- Regularly update your passphrase for added security.  
+- Use tools like **gpg-agent** for easier key management.  
+
+That’s it! You now have a functional GPG key pair set up on Snigdha OS. 🎉