README: spelling stuff, security considerations

Signed-off-by: lucasew <lucas59356@gmail.com>

README.md

@@ -4,20 +4,19 @@ Simple proxy program to allow exposing individual services to a Tailnet, and
 even to the Internet using Tailscale Funnel.
 
 Unfortunately, the Tailscale daemon only allows exposing services using the
-current node domain and you can't spawn (so far) nodes for services. With this
+current node domain, and you can't spawn (so far) nodes for services. With this
 you can!
 
 On first run for one service, you will have to authenticate the service using
 your Tailscale account. The authentication can be either done passing an
 authentication token through the `TS_AUTHKEY` environment or by reading the
 startup logs until you find the authentication link. After authentication,
-tailscale will store the certificates and credentials to the location specified
-by the `-s` flag so subsequent runs will not require reauthentications and up
-to date authorization tokens.
+Tailscale will store the certificates and credentials to the location specified
+by the `-s` flag so subsequent runs will not require reauthentication and up-to-date authorization tokens.
 
 As the [main build of Tailscale](https://tailscale.com/s/serve-headers), you
-can get information about the user acessing the service using the following
-headers that get forwared to the upstream service:
+can get information about the user accessing the service using the following
+headers that get forwarded to the upstream service:
 - `Tailscale-User-Login`
 - `Tailscale-User-Name`
 - `Tailscale-User-Profile-Pic`
@@ -27,6 +26,13 @@ version! It's as safe and stable as
 [tclip](https://github.com/tailscale-dev/tclip) is because this proxy uses the
 exact same primitives.
 
+> **Warning**
+> You can count on the headers sent by ts-proxy as long as you follow the following conditions:
+> - Anything that changes the headers name representation such as Apache with PHP could be cheated
+> by passing the header TAILSCALE_USER_LOGIN, for example.
+> - If some users can access your actual service directly without passing the traffic through ts-proxy
+they can change all the headers they want, including authentication ones.
+
 
 ## Usage