docs: update usage in README

Author: itzg

README.md

@@ -7,25 +7,34 @@ Provides a SAML SP authentication proxy for backend web services
 ## Usage
 
 ```text
-Usage:
-  saml-auth-proxy [flags]
-
-Flags:
-      --attribute-header-mappings stringToString   Comma separated list of attribute=header pairs mapping SAML IdP response attributes to forwarded request header [SAML_PROXY_ATTRIBUTE_HEADER_MAPPINGS] (default [])
-      --authorize-attribute string                 Enables authorization and specifies the attribute to check for authorized values [SAML_PROXY_AUTHORIZE_ATTRIBUTE]
-      --authorize-values strings                   Specifies the possible values that must be present in the authorize attribute [SAML_PROXY_AUTHORIZE_VALUES]
-      --backend-url string                         URL of the backend being proxied [SAML_PROXY_BACKEND_URL]
-      --base-url string                            External URL of this proxy [SAML_PROXY_BASE_URL]
-      --bind string                                host:port to bind for serving HTTP [SAML_PROXY_BIND] (default ":8080")
-  -h, --help                                       help for saml-auth-proxy
-      --idp-ca-path string                         Optional path to a CA certificate PEM file for the IdP [SAML_PROXY_IDP_CA_PATH]
-      --idp-metadata-url string                    URL of the IdP's metadata XML [SAML_PROXY_IDP_METADATA_URL]
-      --name-id-format string                      One of unspecified, transient (default), email, or persistent to use a standard format or give a full URN of the name ID format [SAML_PROXY_NAME_ID_FORMAT]
-      --name-id-mapping string                     Name of the request header to convey the SAML nameID/subject [SAML_PROXY_NAME_ID_MAPPING]
-      --new-auth-webhook-url string                URL of webhook that will get POST'ed when a new authentication is processed [SAML_PROXY_NEW_AUTH_WEBHOOK_URL]
-      --sp-cert-path string                        Path to the X509 public certificate PEM file for this SP [SAML_PROXY_SP_CERT_PATH] (default "saml-auth-proxy.cert")
-      --sp-key-path string                         Path to the X509 private key PEM file for this SP [SAML_PROXY_SP_KEY_PATH] (default "saml-auth-proxy.key")
-      --version                                    version for saml-auth-proxy
+  --attribute-header-mappings value
+    	Comma separated list of attribute=header pairs mapping SAML IdP response attributes to forwarded request header [SAML_PROXY_ATTRIBUTE_HEADER_MAPPINGS]
+  --authorize-attribute string
+    	Enables authorization and specifies the attribute to check for authorized values [SAML_PROXY_AUTHORIZE_ATTRIBUTE]
+  --authorize-values value
+    	Specifies the possible values that must be present in the authorize attribute [SAML_PROXY_AUTHORIZE_VALUES]
+  --backend-url string
+    	URL of the backend being proxied [SAML_PROXY_BACKEND_URL]
+  --base-url string
+    	External URL of this proxy [SAML_PROXY_BASE_URL]
+  --bind string
+    	host:port to bind for serving HTTP [SAML_PROXY_BIND] (default ":8080")
+  --idp-ca-path string
+    	Optional path to a CA certificate PEM file for the IdP [SAML_PROXY_IDP_CA_PATH]
+  --idp-metadata-url string
+    	URL of the IdP's metadata XML [SAML_PROXY_IDP_METADATA_URL]
+  --name-id-format string
+    	One of unspecified, transient (default), email, or persistent to use a standard format or give a full URN of the name ID format [SAML_PROXY_NAME_ID_FORMAT]
+  --name-id-mapping string
+    	Name of the request header to convey the SAML nameID/subject [SAML_PROXY_NAME_ID_MAPPING]
+  --new-auth-webhook-url string
+    	URL of webhook that will get POST'ed when a new authentication is processed [SAML_PROXY_NEW_AUTH_WEBHOOK_URL]
+  --sp-cert-path string
+    	Path to the X509 public certificate PEM file for this SP [SAML_PROXY_SP_CERT_PATH] (default "saml-auth-proxy.cert")
+  --sp-key-path string
+    	Path to the X509 private key PEM file for this SP [SAML_PROXY_SP_KEY_PATH] (default "saml-auth-proxy.key")
+  --version
+    	show version and exit [SAML_PROXY_VERSION]
 ```
 
 The snake-case values, such as `SAML_PROXY_BACKEND_URL`, are the equivalent environment variables