Add documentation (Signing tests certificates)

.gitignore

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 /privkey.pem
+/chap-secrets

README.md

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+#  Docker SSTP server
+
+## Start
+Just run 
+```bash
+docker compose up
+```
+
+
+## Self-signed certificates
+If you need self-signed certificate for testing, you can generate it with following commands:
+
+### Create Root Key
+
+```bash
+openssl genrsa -des3 -out rootCA.key 4096
+```
+
+If you want a non password protected key just remove the `-des3` option
+
+### Create and self sign the Root Certificate
+
+```bash
+openssl req -x509 -new -nodes -key rootCA.key -sha256 -days 1024 -out ca.pem
+```
+
+### Create the server certificate key
+```bash
+openssl genrsa -out privkey.pem
+```
+
+### Create the signing request (csr)
+```bash
+openssl req -new -key privkey.pem -out sstp-csr.csr
+```
+
+### Create a server certificate
+```bash
+openssl x509 -req -in sstp-csr.csr -CA ca.pem -CAkey rootCA.key -CAcreateserial -out cert.pem -days 365
+```