chore: add build instruction

Important note about crypto package:
- We were planning on just using -ldflags to pass privkey and passphrase,
  but that didn't work. So now we are using build tags.
- the var privkey and passphrase are now moved to placeholder and made
  constant.

Author: hakimifr

.gitignore

@@ -1,3 +1,6 @@
+### our own ignored files ###
+crypto/credentials.go
+
 ### dotenv ###
 .env
 

README.md

@@ -1,2 +1,28 @@
 # ksau-go
-The original ksau. Now written in Go!
+
+## Development
+> Table of Content
+> - [Building the Project](#Building-the-Project)
+
+### Building the Project
+To build `ksau-go`, there's one important detail to note. You will need to create
+**crypto/credentials.go**. Then, set constants named `privkey` which is a secret pgp
+key, and `passphrase` which is the passphrase for that secret pgp key (if any),
+else set an empty const.
+
+Follow this template:
+```go
+//go:build credentials
+package crypto
+
+const privkey string = `mykey`
+const passphrase string = "mypassphrase"
+```
+> [!NOTE]
+> The `//go:build credentials` directive is **not** optional. do **not** omit it.
+
+Then, run the following to build:
+```bash
+go build -tags credentials
+```
+

crypto/algo.go

@@ -3,8 +3,6 @@ package crypto
 import "github.com/ProtonMail/gopenpgp/v3/crypto"
 
 var pgp *crypto.PGPHandle = crypto.PGP()
-var passphrase string = "placeholder"
-var privkey string = "placeholder"
 
 func getPrivateKey() *crypto.Key {
 	key, err := crypto.NewPrivateKeyFromArmored(privkey, []byte(passphrase))

crypto/placeholder.go

@@ -0,0 +1,6 @@
+//go:build !credentials
+
+package crypto
+
+const passphrase string = "placeholder"
+const privkey string = "placeholder"